This page was created by the IDL library routine `mk_html_help2`.

Last modified: Sat Jul 10 01:15:15 2010.

# Directory Listing of Routines

# ssl_general/misc

- APPEND_ARRAY
  Append an array to another array. Can also copy an array into a
- ARRAY_CROSS
- AVERAGE_STR
  Average data in res second time segments.
- BIN1D
- BIN2D
- BYTESCALE
- CART_TO_SPHERE
  transform from cartesian to spherical coordinates
- CDF_FILE_NAMES
  Returns an array of filenames within a timerange.
- COLORS_COM
- CROSSP2
  performs cross product on arrays
- CSVECTOR
- DAY_TO_YEAR_DOY
  determines year and day of year given day since 0000 AD
- DIMEN
  Returns the dimensions of an array as an array of integers.
- DIMEN1
- DIMEN2
- DIMEN_SHIFT
  Rotate dimensions of a multidimensional array.
- DIVIDE_DATA
- DOY_TO_MONTH_DATE
  Determines month and date given the year and day of year.
- DPWRSPC
  Called with times time and data quantity, dpwrspc returns a dps
- DYDT_SPIKE_TEST
  This function checks an array for spikes based on its time
- EXTRACT_TAGS
- [4]
  Decimates polylines in an aesthetically pleasing fashion.
- FILE_COPY2
- FILE_DAILYNAMES
- FILE_HTTP_COPY
  Downloads file(s) from http servers.
- FILE_OPEN
- FILE_RETRIEVE
- FILE_RETRIEVE_V
- FILE_SOURCE_DIRNAME
- FILE_TOUCH
- FIND_CONST_INTERVALS
- FIND_STR_ELEMENT
- FNAME_TO_TIME
  To translate the name of a standard WIND data file into the starting
- GET_COLORS
- GET_FILE_NAMES
  Gets an array of filenames within a time range
- GET_FILE_NAMES_IND
  Gets an array of filenames within a masterfile within a time range
- GET_RT_PATH
  gets the directory of the calling routine. Used for reliably looking
- GRAD
- HIGH_PASS_FILTER
  subtracts running average from a data array
- HISTBINS
- HISTBINS2D
- INTERP
  Linearly Interpolates vectors with an irregular grid.
- MAKEGIF
  Creates a GIF file from the currently displayed image.
- MAKEJPG
  Creates a jpg file from the currently displayed image.
- MAKEPNG
  Creates a PNG file from the currently displayed image.
- MAKEPS.PRO
- MINMAX
- MK_HTML_HELP2
  Creates a html document from a list of IDL procedures.
- NDIMEN
  Returns the number of dimensions in an array.
- NN
- OPLOT_ERR
  Plot error bars over a previously drawn plot.
- PCLOSE
- PLOT_POSITIONS
  Procedure that will compute plot positions for multiple plots per page.
- POPEN
  Change plot device to postscript.
- POPEN_COM
- PRINT_OPTIONS
- PRINTDAT
  Displays information and contents of a data variable. (Very similar to HELP procedure but much more verbose.)
- PTR_EXTRACT
- PTRACE
- PWRSPC
  Called with times time and data quantity, PWRSPC returns a power
- SETBP
- SHARE_COLORS
  Procedure that allows multiple IDL sessions to share the same color table.
- SMOOTH_IN_TIME
  Runs smooth for irregular grids, after regularising grid
- SPACE_BAR
- SSL_CORRELATE_TPLOT
  Identified the amount of shift required to correlate two
- SSL_CORRELATION_SHIFT
  Calculates the shift required to correlate two tme series of
- SSL_SET_COMPLEMENT
- SSL_SET_INTERSECTION
- SSL_SET_UNION
- SSL_TIME_CHECK
- STR2TIME
- STR_ELEMENT
  Find (or add) an element of a structure.
- STRFILTER
  Returns the subset of stringarray that matchs searchstring
- STRIPPATH
- STRUCT_VALUE
- TAG_NAMES_R
- TCLIP
  wapper for xclip.pro allowing input of tplot variable names
- TDEFLAG
  wapper for xdeflag.pro allowing input of tplot variable names
- TDEGAP
  wrapper for xdegap.pro allowing input of tplot variable names
- TDESPIKE_AE
- TDPWRSPC
  wapper for dpwrspc.pro allowing input of a tplot variable name
- THIGH_PASS_FILTER
  Uses high_pass_filter to calculate a running average of the input data and
- TIME_AVERAGE
- TIME_CLIP
- TIME_DOUBLE
  A fast, vectorized routine that returns the number of seconds since 1970.
- TIME_EPOCH
  Returns the EPOCH time required by CDF files.
- TIME_PB5
  Returns the PB5 time required by CDF files.
- TIME_STAMP
  Prints a time stamp along the lower right edge of the current plot box
- TIME_STRING
  Converts time to a date string.
- TIME_STRUCT
  A fast, vectorized routine that returns a time structure.
- TIME_TICKS
  Returns a structure that can be used to create time ticks for a plot.
- TKM2RE
- TPWRSPC[2]
  wrapper for pwrspc.pro allowing input of a tplot variable name.
- TRANGE_STR
- TSMOOTH_IN_TIME
  Calls smooth_in_time function on a plot variable
- AVSIG
  Average and dispersion of an array, zeros can be not included,
- TSUB_AVERAGE
  Subtracts average or median values from the data in a tplot
- STRING_PARSER
  Parse strings into components
- CODE_FRAGMENT
  takes a string, where input variables are defined as array_elements
- TVECTOT
- UNDEFINED
  Tests whether a variable is undefined
- WI
- XCLIP
  Replaces with FLAGs the values of the array that are BEYOND
- XDEFLAG
  Replaces FLAGs in arrays with interpolated or other values
- XDEGAP
  Locates gaps in data, and fills in with NaN

# Routine Descriptions

## APPEND_ARRAY

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    PROCEDURE: append_array, a0, a1
    PURPOSE:
       Append an array to another array.  Can also copy an array into a
       subset of another.
    INPUT:
       a0:   Array to modify.
       a1:   Array to append to, or copy into, a0.
    KEYWORDS:
       index:    Index of a0 at which to append or copy a1.  If index is
         greater than the number of elements of a0, then
         a0 is enlarged to append a1. Returns the index of the first
         element of a0 past the section copied from a1.
       done: If set, make a0 equal to the first index elements of a0.
    CREATED BY:    Davin Larson
    LAST MODIFIED: @(#)append_array.pro    1.6 98/08/13

(See ssl_general/misc/append_array.pro)

## ARRAY_CROSS

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     FUNCTION array_cross(l1,l2)
     Purpose:
        returns a 2*n array, where n = n_elements(l1)*n_elements(l2)
        each pair is a combination of l1 and l2
        the total list represents all possible pairings of l1 and l2

     Written by Patrick Cruce

     $LastChangedBy: pcruce $
     $LastChangedDate: 2009-03-11 11:10:36 -0700 (Wed, 11 Mar 2009) $
     $LastChangedRevision: 5255 $
     $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/array_cross.pro $

(See ssl_general/misc/array_cross.pro)

## AVERAGE_STR

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    FUNCTION:	average_str(data, res)
    PURPOSE:
    	Average data in res second time segments.
    INPUTS:
    	DATA:	array of structures.  One element of structure must be TIME.
    	RES:	resolution in seconds.
    KEYWORDS:
    	NAN:	If set, treat the IEEE NAN value as missing data.
    CREATED BY:	Davin Larson
    LAST MODIFIED:	%W% %E%

(See ssl_general/misc/average_str.pro)

## AVSIG

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     NAME:
         avsig
     PURPOSE:
         Average and dispersion of an array, zeros can be not included,
         handles NaN values correctly
     CALLING SEQUENCE:
         xbar = Avsig(x, sigma = sigma, no_zeros = no_zeros, $
                    sig_mean = sig_mean, dimension = dimension, $
                    fractional = fractional, median = median, $
                    _extra = _extra)
     INPUT:
         x = an array
     OUTPUT:
         xbar = mean, total(x)/n_elements(x)
     KEYWORDS:
         no_zeros= if set, strip out zeros
         get_sigma = if set, calculate the standard deviation
         sigma = standard deviation, sqrt(total((x-xbar)^2/(nx-1)))
         sig_mean = if set return sigma/sqrt(nx), the standard deviation of the
                    mean of the array,
         dimension = the dimension of the array to find the mean in,
                     passed into the total command, it must be a scalar.
         fractional = if set, the fractional error is passed out as sigma,
                      don't use this if zero is a valid value of xbar...
         median = if set, use the median instead of the mean for xbar, it
                  is not recommended fo sigma calculations
     HISTORY:
         12-9-94, jmm, jimm@ssl.berkeley.edu
         2-13-95, jmm, added dimension keyword, switched from ok_zeros to no_zeros
         5-sep-1996, jmm, switched to double precision
         7-oct-2008, jmm, ignores NaN values, added median keyword

(See ssl_general/misc/tsub_average.pro)

## BIN1D

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     Procedure: bin1d

     Purpose:
    Uses histogram to bin data according to array binarr. The elements in binarr
     that are in a specific bin correspond to elements in other arrays (like
     density, temperature etc) and the averages of those are computed within
     each bin. The arrays to be averaged within each bin are passed in
     arrs2bin(NXM) where N is the number of elements of the binarr and M is the
     number of quantities.

     Output: kinbin is K-array of elements (K=number of bins) containing
             number of points within each bin, bincenters a K-array with center
             of bins, averages is KXM array with averages (zero if no points)
             stdevs an KXM array with stdevs about the mean and medians is
             KXM array of medians within each bin

     If any of the keywords maxvarvec or minvarvec is set to a name
     then it is assumed that the first two
     elements of the array "arrs2bin" correspond to the X,Y coordinates of
     a "flow" field. The corresponding data in each cell will be rotated
     in a max/min variance direction. The maxvariance direction will
     be in 2D vector maxvarvec for each cell. The minvariance direction
     will be in 2D vector minvarvec for each cell. The vector norm is the
     variance in the max/min direction, i.e.,
     lambda_i=sqrt(maxvarvec(*,0)^2+maxvarvec(*,1)^2).

     if keyword flag4nodata is set, then points with no data are flags set equal
     to the value passed in, not zeros.

     Usage:
    ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
     bin1D,Ygse,[[Ni],[Ti],[Vx],[fx],[Qx],[Eylep]],-15.,15.,1.,kinbin,Ycntrs,avrg,std,med
     Niavg=avrg(*,0)&Tiavg=avrg(*,1)&Vxavg=avrg(*,2)&fxavg=avrg(*,3)&Qxavg=avrg(*,4)&Eylepavg=avrg(*,5)
    ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
     $LastChangedBy: pcruce $
     $LastChangedDate: 2007-10-03 14:49:09 -0700 (Wed, 03 Oct 2007) $
     $LastChangedRevision: 1661 $
     $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/idl_socware/trunk/external/IDL_GEOPACK/t01/t01.pro $

(See ssl_general/misc/bin1d.pro)

## BIN2D

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     Procedure: bin2d

     Purpose:
     A slightly simpler wrapper for vassilis's routine for 2-d binning
     NOTE: despite the fact that they are keywords either binsize or
     binnum must be set for the proceedure to function

     Inputs:
         x: the x components for the bins. Should be
               an N length array.
         y:  the y components for the bins. Should be an
               N length array.
         arrs2bin: the arrays to be binned should be an NxM
                   sized array or an N sized array
                   (Note: Interpolation to match the N component
                    of input arrays is the responsibility of the
                    user.)

     Keywords:

         binsize: a number or a 2 element array.  If a single number
                  it will be treated as size of the bins for the x dimension
                  and the y dimension.  If it is a two element array, the
                  first element will be the size of the bins on the x
                  axis and the second element will be the size of the
                  bins on the y axis.
                  Warning: Either Binsize or binum must always be set.

         binum: a number of 2 element array.  If a single number it
                 will be treated as the number of bins on for both
                 axes.  If a 2 element array, the first element is
                 number of bins on the x-axis and the second element is
                 the number of bins on the y-axis. (Note: The number of
                 bins actually produced may vary by +- 1) Bins will be
                 evenly spaced over xrange and yrange if provided, and
                 over the range of the data if not.

                 Warning: Either Binsize or binum must always be set.

         xrange,yrange(optional): a 2 element array specifying the min
                 and the max over which binning will occur for the
                 respective axis(default: all data)

         flagnodata(optional): set this keyword to a flag to replace
                 output values with if there is no data. (default: 0)

         averages(output): outputs 2-d array in which the bin averages
                       are stored

         medians(output): outputs 2-d array in which the bin medians are stored

         stdevs(output): outputs 2-d array in which the bin stdevs are stored.

         binhistogram(output): a 2-d histogram of the number of elements
                 used for constructing each cell

         xcenters,ycenters(output): 1-d array of the centers for the bins
                 on each axis.

         minvarvec,maxvarvec(output): Either of these are set arrs2bin
                 will must have dimension M >= 2. The first 2 arrays
                 of the M dimension(ie arrs2bin[*,0] and arrs2bin[*,1]
                 will be treated as corresponding elements of an X,Y flow
                 field. The maxvariance direction will be a 2D vector in
                 maxvarvec for each cell. The minvariance direction
                 will be a 2D vector in minvarvec for each cell. The
                 vector norm is the variance in the max/min direction, i.e.,
                 lambda_i=sqrt(maxvarvec(*,0)^2+maxvarvec(*,1)^2).

     Notes and Warnings:
       1.  Interpolation to match the N component of input arrays is the
           responsibility of the user.

       2.  The number of bins actually produced may vary by +- 1 from the
           number requested by binum

       3.  Either binsize or binum must always be set.

       4.  If both binsize and binum, binsize will take precedent.

      SEE ALSO: bin1d.pro,plotxyz.pro,thm_crib_plotxyz.pro

     $LastChangedBy: pcruce $
     $LastChangedDate: 2008-02-06 13:43:58 -0800 (Wed, 06 Feb 2008) $
     $LastChangedRevision: 2352 $
     $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/tplot/tplotxy.pro $

(See ssl_general/misc/bin2d.pro)

## BYTESCALE

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    FUNCTION:  bytescale(array)
    PURPOSE:   Takes an array or image and scales it to bytes
    INPUT:     array of numeric values.
    KEYWORDS:
       RANGE:  Two element vector specifying the range of array to be used.
            Defaults to the min and max values in the array.
       ZERO:   Forces range(0) to zero
       TOP:    Maximum byte value  (default is !d.table_size-2)
       BOTTOM: Minimum byte value  (default is 1)
       MIN_VALUE: autoranging ignores all numbers below this value
       MAX_VALUE: autoranging ignores all numbers above this value
       MISSING:  Byte value for missing data. (values outside of MIN_VALUE,
         MAX_VALUE range)  If the value is less than 0 then !p.background is used.
       LOG:    sets logrithmic scaling

    CREATED BY:	Davin Larson
    LAST MODIFICATION:	@(#)bytescale.pro	1.22 02/04/17

(See ssl_general/misc/bytescale.pro)

## CART_TO_SPHERE

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    PROCEDURE:  cart_to_sphere, x, y, z,  r, theta, phi
    PURPOSE:
                transform from cartesian to spherical coordinates
    INPUTS:     x, y, z          (array or scalar)
    OUTPUTS:    r, theta, phi    (same as x,y,z)
    KEYWORDS:   ph_0_360:   if positive, 0<=phi<=360, if zero, -180<=phi<=180,
                            ***if negative, best guess phi range returned***
                ph_hist:   a two element array of max and min values for phi.
                            eg: if ph_0_360 is not set, and ph_hist=[-220,220]
                                then if d(phi)/dt is positive near 180, then
                                phi => phi+360 when phi passes the 180/-180
                                discontinuity until phi reaches 220.
                CO_LATITUDE:  If set theta will be in co-latitude. (0<=theta<=180)
                MIN_VALUE:
                MAX_VALUE:
    CREATED BY:	Davin Larson
    LAST MODIFICATION:	@(#)cart_to_sphere.pro	1.13 02/04/17

    NOTES:
       -90 < theta < 90   (latitude not co-lat)

(See ssl_general/misc/cart_to_sphere.pro)

## CDF_FILE_NAMES

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    FUNCTION: cdf_file_names
    PURPOSE:
       Returns an array of filenames within a timerange.
    USAGE:
       files=cdf_file_names(FORMAT,trange=trange,/verbose)
    INPUT:
       FORMAT is a string that will be interpreted as one of two things:
         CASE 1:
            e.g.    FORMAT = '/home/wind/dat/wi/3dp/k0/????/wi_k0_3dp*.cdf'
            if FORMAT contains * or ? then filenames are returned that match that
            pattern and for which YYYYMMDD falls within the specified timerange.
            for example:
            (UNIX only)
         CASE 2:
            e.g.    FORMAT = 'fa_k0_ees_files'
            The name of an indexfile that associates filenames with start and
            end times. If his file is not found, then the environment variable
            getenv('CDF_INDEX_DIR') is prepended and searched for.
            See "make_cdf_index" for information on producing this file.
         SPECIAL NOTE:
            If strupcase(FORMAT) is the name of an environment varible. Then
            the value of that environment variable is used instead.
    KEYWORDS:
         TRANGE:
            Two element array specifying the time range for which data files should
            be returned.  If not provided then "timerange" is called to provide
            the time range.  See also "timespan".
         NFILES:
            Named variable that returns the number of files found.
         VERBOSE:
            Set to print some useful info.
         FILEINFO:  OBSOLETE!
            Set to a named variable that will return a table of file info.
    NOTES:
         UNIX only!

(See ssl_general/misc/cdf_file_names.pro)

## CODE_FRAGMENT

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    NAME:
     code_fragment
    PURPOSE:
     takes a string, where input variables are defined as array_elements
     'qq' and creates a set of tplot commands using those data
    CALLING SEQUENCE:
     code_fragment,  inp_string,  otp_string
    HISTORY:
     13-jun-2007, jmm, jimm@ssl.berkeley.edu

(See ssl_general/misc/tuserdef.pro)

## COLORS_COM

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    COMMON BLOCK  colors_com
    WARNING!  Don't rely on this file to remain stable!
    USE "get_colors" to get color information.
    SEE ALSO:
      "get_colors","bytescale","loadct2"
    CREATED BY: Davin Larson
    File:      96/08/30
    Version:   1.2
    Last Mod:  colors_com.pro

(See ssl_general/misc/colors_com.pro)

## CROSSP2

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    FUNCTION:	crossp2(a,b)
    INPUT:
    	a,b:	real(n,3)	vector arrays dimension (n,3) or (3)
    PURPOSE:
    	performs cross product on arrays
    CREATED BY:
    	J.McFadden	97-3-14
    Modifications
    	J.McFadden	05-2-7 changed first if to "if ndimen(a) eq 1 and ndimen(b) eq 1"

(See ssl_general/misc/crossp2.pro)

## CSVECTOR

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     Function: csvector

     Purpose:  This procedure implements the create,add, and read
               methods for a traditional computer science
               data structure: the vector.The vector
               list of elements of any type and of any length.

               Advantages over array:
               1. store heterogenous elements of any type in a list.
               2. Lists can grow as large as memory and you don't
               need to know how big it will be in advance
               3. You don't need to worry about how the data is stored

               Disadvantages over array:
               1. You can't directly apply operations to the data
               structure
               2. You are forced to use abstraction

               Inputs: arg1:the meaning of the argument varies with syntax
                       arg2:the meaning of the argument varies with syntax

               Keywords: read(optional): set this if you want
                                         to read an element
                         length(optional): set this if you want
                                           to read the length
                         free(optional): set this if you want to free the
                                         vector's memory without
                                         creating a leak, it will return
                                         the number of elements free'd

               Outputs: a vector, the internal representation is
               abstracted, use the methods to access this data structure

               Syntax(each method is followed by examples):

                       create:
                         v = csvector(some_element)
                         v = csvector(1)
                         v = csvector([1,2])
                         v = csvector({a:1,b:2})
                       add:
                         vector = csvector(some_element,vector)
                         v = csvector(1,v)
                         v = csvector('a',v)
                         v = csvector([1,2],v)
                       read:
                         element = csvector(element_index,vector,/read)
                         e = csvector(0,v,/read) ;first element
                         e = csvector(csvector(v,/L)-1,v,/r) ;last element
                       length:
                         length = csvector(vector,/length)
                         l = csvector(v,/l)
                         l = csvector(v,/length)
                       free:
                         num = csvector(vector,/free)
                         temp = csvector(v,/free)

           NOTES: in the event of overflow during add the vector.a
           component will double in size

           Add/Create stores a copy of the element not the element itself

           If you want to do manual lengths and reads you can look
           at the code, but I would recommend against cause you are
           violating abstraction which means the internal representation
           could change and invalidate your code.

           This might be worth writing in O.O. idl as well

           To get type flexibility it uses a pointer for every object
           Thus if you aren't careful this function will eat your
           system memory for breakfast.  Use heap_gc to clean up if you
           are running out of memory.

(See ssl_general/misc/csvector.pro)

## DAY_TO_YEAR_DOY

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    NAME:
       day_to_year_doy
    PURPOSE:
       determines year and day of year given day since 0000 AD
    USAGE:
       day_to_year_doy,daynum,year,doy
    INPUT:
       daynum:   (long int)  day since 0 AD
    OUTPUT:
       year:     year         (0 <= year <= 14699 AD)
       doy:      day of year  (1 <= doy  <=  366)
    NOTES:
      This procedure is reasonably fast, it works on arrays and works from
      0 AD to 14699 AD

    CREATED BY:	Davin Larson  Oct 1996
    FILE:  day_to_year_doy.pro
    VERSION:  1.2
    LAST MODIFICATION:  97/01/27

(See ssl_general/misc/day_to_year_doy.pro)

## DIMEN

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    FUNCTION:   dimen(x)
    PURPOSE:
      Returns the dimensions of an array as an array of integers.
    INPUT:  matrix
    RETURNS:  vector of dimensions of matrix.
       If the input is undefined then 0 is returned.
       if the input is a scaler then 1 is returned.

    SEE ALSO:  "dimen", "data_type", "dimen1", "dimen2"

    CREATED BY:	Davin Larson
    LAST MODIFICATION:	@(#)dimen.pro	1.6 96/12/16

(See ssl_general/misc/dimen.pro)

## DIMEN1

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    FUNCTION:   dimen1
    INPUT:  matrix
    RETURNS:  scaler int:  size of first dimension  (1 if dimension doesn't exist)

    CREATED BY:	Davin Larson
    LAST MODIFICATION;	@(#)dimen1.pro	1.3 95/08/24

(See ssl_general/misc/dimen1.pro)

## DIMEN2

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    FUNCTION:   dimen2
    INPUT:  matrix
    RETURNS:  scaler int:  size of second dimension  (1 if dimension doesn't exist)

    CREATED BY:	Davin Larson
    LAST MODIFICATION;	@(#)dimen2.pro	1.3 95/08/24

(See ssl_general/misc/dimen2.pro)

## DIMEN_SHIFT

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    FUNCTION:  dimen_shift(x,shift)
    NAME:
      dimen_shift
    PURPOSE:
      Rotate dimensions of a multidimensional array.
      This function is very similar to transpose but works on multi-dimensional
      arrays to shift the dimensions around.
      It has no effect on scalars and one dimensional arrays.
    INPUT:
      x   multi-dimensional array of any type
      shift:  1 or -1  direction of shift.
    CREATED BY: Davin Larson
    LAST MODIFICATION:	@(#)dimen_shift.pro	1.4 98/07/09

(See ssl_general/misc/dimen_shift.pro)

## DIVIDE_DATA

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    PROCEDURE:	divide_data

    PURPOSE:

      Divides successive channels of SST data by powers of 'factor', to

      separate the traces. Also, optionally, multiplies data by an overall factor,

      'conv_factor', to convert units.

    INPUT:		in_name (string), the name of the input TPLOT variable
    			structure.
                   out_name (string), the name of the output TPLOT variable
    			structure.

    KEYWORDS:      factor (float), by which fluxes in successive channels are

                   	divided.
    		conv_factor (optional float), by which fluxes in all channels
    			are multiplied.

    CREATED BY:	Ted Freeman

    FILE:  divide_data.pro

    LAST MODIFIED:  @(#)divide_data.pro	1.2 99/09/01

    NOTES:	  "LOAD_3DP_DATA" and "GET_SPEC" must be called first.

(See ssl_general/misc/divide_data.pro)

## DOY_TO_MONTH_DATE

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    PROCEDURE:
      doy_to_month_date, year, doy, month, date
    NAME:
      doy_to_month_date
    PURPOSE:
     Determines month and date given the year and day of year.
     fast, vector oriented routine that returns the month and date given year and
     day of year (1<=doy<=366)

    CREATED BY:	Davin Larson  Oct 1996
    FILE:  doy_to_month_date.pro
    VERSION:  1.2
    LAST MODIFICATION:  97/01/27

(See ssl_general/misc/doy_to_month_date.pro)

## DPWRSPC

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    NAME:
     dpwrspc
    PURPOSE:
        Called with times time and data quantity, dpwrspc returns a dps
        spectrum at frequencies fdps. A Hanning window is applied to the
        input data, and its power is divided out of the returned
        spectrum. A straight line is subtracted from the data to reduce
        spurious power due to sawtooth behavior of a background. UNITS
        ARE (UNITS)^2 WHERE UNITS ARE THE UNITS OF time. fdps is in
        Hz. THUS THE OUTPUT REPRESENTS THE MEAN SQUARED AMPLITUDE OF THE
        SIGNAL AT EACH SPECIFIC FREQUENCY. THE TOTAL (SUM) POWER UNDER
        THE CURVE IS EQUAL TO THE MEAN (OVER TIME) POWER OF THE
        OSCILLATION IN TIME DOMAIN. NOTE: IF KEYWORD notperhz IS SET,
        THEN POWER IS IN UNITS OF NT^2 ELSE IT IS IN UNITS OF NT^2/HZ.
    CALLING SEQUENCE:
     dpwrspc, time, quantity, tdps, fdps, dps, nboxpoints = nboxpoints, $
              nshiftpoints = nshiftpoints, bin = bin, tbegin = tbegin,$
              tend = tend, noline = noline, nohanning = nohanning, $
              notperhz = notperhz
    INPUT:
     time = the time array
     quantity = the function for which you want to obtain a power
                spectrum
    OUTPUT:
     tps = the time array for the dynamic power spectrum
     fdps = the frequency array (units =1/time units)
     dps = the power spectrum, (units of quantity)^2/frequency_units
    KEYWORDS:
     nboxpoints = the number of points to use for the hanning window, the
                  default is 256
     nshiftpoints = the default is 128
     bin = a binsize for binning of the data along the frequency domain,
           the default is 3
     tbegin = a start time, the default is time[0]
     tend = an end time, the default is time[n_elements(time)-1]
     noline = if set, no straight line is subtracted
     nohanning = if set, then no hanning window is applied to the input
     notperhz = if set, the output units are simply the square of the
                input units
     noTmVariance = if set replaces output spectrum for any windows that
                    have variable cadence with NaNs
     tm_sensitivity = If noTmVariance is set, this number controls
                             how much of a dt anomaly is accepted. The
                             program will flag a time resolution
                             discontinuity if the time resolution dt
                             changes by a value greater than
                             dt/dt_sensitivity; the default
                             is 100.0; i.e. If, for a given spectrum, if
                             there are points with abs(dt[i]-median(dt)
                             Gt median(dt)/100.0, then this will
                             be set to NaN. A larger value means
                             more sensitivity. If you want to flag round-off
                             errors then try a value of 1.0e8.
     fail = if set to a named variable, returns 1 if an error occurs, 0 otherwise

    $LastChangedBy: $
    $LastChangedDate: $
    $LastChangedRevision: $
    $URL: $

(See ssl_general/misc/dpwrspc.pro)

## DYDT_SPIKE_TEST

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    NAME:
     dydt_spike_test
    PURPOSE:
     This function checks an array for spikes based on its time
     derivative. This is designed mostly for THEMIS GMAG spikes that
     persist over multiple data points, but should work on single data
     point spikes too.
    CALLING SEQUENCE:
     flag = dydt_spike_test(t0, y0, dydt_lim = dydt_lim, $
                            sigma_y = sigma_y, nsig = nsig, $
                            no_degap = no_degap, pad=pad, $
                            degap_margin = degap_margin, $
                            degap_dt = degap_dt, _extra = _extra)
    INPUT:
     t0 = a time array
     y0 = a data aray, same number of elements as t0
    OUTPUT:
     flag = a bytarr(n_elements(t0)), set to 1 for spikes, 0 for ok data,
            note that NaN values are automatically set to 1
    KEYWORDS:
     dydt_lim =  a value for the max. allowed derivative, the default is
                 to calculate a limiting value from the uncertainty in
                 the data.
     sigma_y = if known, an estimate of the standard deviation in y0
               values. The default is to use sqrt(y), as if you have a
               photon count for data. If you do not know
               this uncertainty in Y, it might be a good idea to use
               dydt_lim.
     nsig = the number of uncertainties in dydt that will be used to
            obtain the limit value at each data point.
     pad = pad the spike flag on either side by this many data points.
     no_degap = By default, the program calls xdegap and xdeflag routines
                to deal with gaps in the data. Set this keyword to avoid
                this.
    DEGAP KEYWORDS:
     nowarning = if set, suppresses warnings
     maxgap = the maximum gap size filled, in seconds
     degap_dt = a time_interval for the degap process, the default is to
                use the minimum of the time resolutions in the data,
                i.e., min(t0[1:*]-t0)
     degap_margin = a margin value for the degap call, the default is to
                    use the minimum of the time resolutions in the data,
                    i.e., min(t0[1:*]-t0)

    HISTORY:
     7-apr-2008, jmm, jimm@ssl.berkeley.edu

    $LastChangedBy: jimm $
    $LastChangedDate: 2008-04-14 10:44:44 -0700 (Mon, 14 Apr 2008) $
    $LastChangedRevision: 2705 $
    $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/dydt_spike_test.pro $

(See ssl_general/misc/dydt_spike_test.pro)

## EXTRACT_TAGS

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    PROCEDURE:  extract_tags, newstruct, oldstruct
    PURPOSE: takes the named tag elements from oldstruct and puts them into
       newstruct.  This procedure is very useful for creating a structure that
       can be passed onto the PLOT or OPLOT subroutines using the _EXTRA keyword.
       If no tag keywords are included then all tag elements of oldstruct are
       added to newstruct.  The mode keyword PRESERVE is used to prevent the
       overwritting of an existing keyword.
    INPUTS:
      newstruct:  new structure to be created or added to.
      oldstruct:  old structure from which elements are extracted.
    KEYWORDS:  Only one of the following should be given:;
     (TAG KEYWORDS)
      TAGS:  array of strings.  (tag names) to be taken from oldstruct and put in
          newstruct
      EXCEPT: array of strings.  Tag names not to be copied from old to new.
      OPLOT:  (flag)  If set, then TAGS is set to an array of valid keywords
         for the OPLOT subroutine.
      PLOT:   (flag)  If set, then TAGS is set to an array of valid keywords
         for the PLOT subroutine.
      CONTOUR: (flag) If set, then TAGS is set to an array of valid keywords
         for the CONTOUR procedure.   (might not be complete)
    If no KEYWORDS are set then all elements of oldstruct are put into newstruct
      (MODE KEYWORDS)
      PRESERVE: (flag) Prevents the overwritting of an existing, non-null keyword.
         Adds tags to newstruct that were not already there, or if they were there
         and their values were either "" or 0.
    CREATED BY:	Davin Larson
    FILE:  extract_tags.pro
    VERSION  1.21
    LAST MODIFICATION: 02/04/17

(See ssl_general/misc/extract_tags.pro)

## FILE_COPY2

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     Procedure: file_copy2

(See ssl_general/misc/file_copy2.pro)

## FILE_DAILYNAMES

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      Procedure:  FILE_DAILYNAMES
      Author: Davin Larson

(See ssl_general/misc/file_dailynames.pro)

## FILE_HTTP_COPY

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      WARNING: the interface to this routine is not yet solidified. Use the wrapper routine:
      file_retrieve instead. This routine is still under development.

     NAME:
        file_http_copy

     PURPOSE:
        Downloads file(s) from http servers.
        Also performs Searches without download.
        Copies the file to a user specified local directory.
        By default, files are only downloaded if the remote file is newer than
        the local file (based on mtime) or if the files differ in size.
        This routine is intended for use with simple HTTP file servers.
        Wildcard matching and recursive file searching can be used as well.

     CALLING SEQUENCE: There are two methods:
     Method 1:
        FILE_HTTP_COPY, pathnames, SERVERDIR=serverdir, LOCALDIR=localdir
        where:
          pathnames = (input string(s), scaler or array)  Relative path name of file to download.;
          serverdir = (scaler input string)  Root name of source URL, must
                                             begin with: 'http://' and end with '/'
          localdir  = (scaler input string)  Root name of local directory, typically
                                             ends with '/'
        Note:   The source is at:    serverdir + pathnames
                The destination is:  localdir + pathnames
     Method 2:
        FILE_HTTP_COPY, URL
           URL = full URL(S) of source file
           Directory structure is not retained with this procedure

     Example:
        FILE_HTTP_COPY, 'ssl_general/misc/file_http_copy.pro',  $
                  SERVERDIR='http://themis.ssl.berkeley.edu/data/themis/socware/bleeding_edge/idl/' $
                  localdir = 'myidl/'

        Note: Unix style directory separaters '/' should be used throughout. This convention will still
              work with WINDOWS.

     Alternate calling sequence:
        FILE_HTTP_COPY,URL
            where URL is an input (string) such as:  URL = '

     INPUTS:
          URL - scalar or array string giving a fully qualified url

     OPTIONAL KEYWORDS:
         NO_CLOBBER:   (0/1) Set this keyword to prevent overwriting local files.
         IGNORE_FILESIZE: (0/1) Set this keyword to ignore file size when
               evaluating need to download.
         NO_DOWNLOAD:  (0/1) Set this keyword to prevent file downloads (url_info
               is still returned)
         URL_INFO=url_info: (output) Named variable that returns information about
               remote file such as modification time and file size as determined
               from the HTML header. A zero is returned if the remote file is
               invalid.
         FILE_MODE= file_mode:     If non-zero, sets the permissions for downloaded files.
         DIR_MODE = dir_mode:      Sets permissions for newly created directories
                                (Useful for shared directories)
         ASCII_MODE:  (0/1)   When set to 1 it forces files to be downloaded as ascii text files (converts CR/LF)
                              Setting this keyword will force ignore_filesize keyword to be set as well because
                              files will be of different sizes typically.
         VERBOSE:      (input; integer) Set level of verboseness:   Uses "DPRINT"
               0-nearly silent;  2-typical messages;  4: debugging info

     Examples:
       ;Download most recent version of this file to current directory:
       FILE_HTTP_COPY,'http://themis.ssl.berkeley.edu/data/themis/socware/bleeding_edge/idl/ssl_general/misc/file_http_copy.pro'

     OPTIONAL INPUT KEYWORD PARAMETERS:
           PATHNAME = pathname   ; pathname is the filename to be created.
                    If the directory does not exist then it will be created.
                    If PATHNAME does not exist then the original filename is used
                    and placed in the current directory.
    ;
     RESTRICTIONS:

         PROXY: If you are behind a firewall and have to access the net through a
             Web proxy,  set the environment variable 'http_proxy' to point to
             your proxy server and port, e.g.
             setenv,  'http_proxy=http://web-proxy.mpia-hd.mpg.de:3128'

                   The URL *MUST* begin with "http://".

     PROCEDURE:
         Open a socket to the webserver and download the header.

     EXPLANATION:
         FILE_HTTP_COPY can access http servers - even from behind a firewall -
         and perform simple downloads. Currently,
         Requires IDL V5.4 or later on Unix or Windows, V5.6 on
         Macintosh

     EXAMPLE:
          IDL> FILE_HTTP_COPY,'http://themis.ssl.berkeley.edu/themisdata/thg/l1/asi/whit/2006/thg_l1_asf_whit_2006010103_v01.cdf'
          IDL> PRINTDAT, file_info('thg_l1_asf_whit_2006010103_v01.cdf')
          or

     MINIMUM IDL VERSION:
         V5.4  (uses SOCKET)
     MODIFICATION HISTORY:
       Original version:  WEBGET()
         Written by M. Feldt, Heidelberg, Oct 2001 <mfeldt@mpia.de>
         Use /swap_if_little_endian keyword to SOCKET  W. Landsman August 2002
         Less restrictive search on Content-Type   W. Landsman   April 2003
         Modified to work with FIRST image server-  A. Barth, Nov 2006
       FILE_HTTP_COPY:   New version created by D Larson:  March 2007.
         Checks last modification time of remote file to determine need for download
         Checks size of remote file to determine need to download
         Very heavily modified from WEBGET():
       May/June 2007 - Modified to allow file globbing (wildcards).
       July 2007   - Modified to return remote file info  (without download)
       July 2007   - Modified to allow recursive searches.
       August 2007 - Added file_mode keyword.
       April  2008 - Added dir_mode keyword
       Sep 2009    - Fixed user-agent

     $LastChangedBy: davin-win $
     $LastChangedDate: 2009-09-25 17:35:21 -0700 (Fri, 25 Sep 2009) $
     $LastChangedRevision: 6782 $
     $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/file_http_copy.pro $

(See ssl_general/misc/file_http_copy.pro)

## FILE_OPEN

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    Procedure  FILE_OPEN,type,name
    Purpose:  wrapper for  OPENW, OPENU, OPENR,  FILE_MKDIR
    type must be one of:  'w', 'u', 'r',  'd'  (write, update, read, directory)
       This procedure performs the functions of creating/opening files and creating directories.
       It has several useful features which the regular procedures do not have:
      1)  Non-existant directories are created automatically (with optional mode setting)
      2)  If a non-existant file is opened for update, it is created with OPENW instead of producing an error.
      3)  Files (or directories) can be tested to see if they can be created before actually opening (or creating)
               them (use the TEST keyword). (The returned structure INFO will have the WRITE element set)

    Example 1:   Creating a file for write access:
       FILE_OPEN,'w','/dir1/dir2/dir3/file.tmp',unit=u  ; Will create the director tree if it does not already exist.
    Example 2:   Creating new directories with defined modes:
       FILE_OPEN,'d','/dir1/dir2/dir3', dir_mode="777 ,
         All newly created directories will have the given permissions  (Octal 777)
    Example 3:
       FILE_OPEN,'w','/dir1/dir2/dir3/file.tmp',/test,info=info  ;This will test if the file
              can be created (with given file system permissions) without actually creating the file.
              The returned info stucture can potentially have info.exists eq to 0 and info.write eq 1
    Example 4:

(See ssl_general/misc/file_open.pro)

## FILE_RETRIEVE

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    FUNCTION file_retrieve(pathnames,local_data_dir=local_data_dir)
    Keywords:
        local_data_dir:  local data directory;    'must end with a '/'
        remote_data_dir:  remote data directory:  'must end with a  '/'

    $LastChangedBy: davin-win $
    $LastChangedDate: 2009-09-25 17:35:21 -0700 (Fri, 25 Sep 2009) $
    $LastChangedRevision: 6782 $
    $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/file_retrieve.pro $

(See ssl_general/misc/file_retrieve.pro)

## FILE_RETRIEVE_V

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    Procedure: file_retrieve_v

    Purpose:  Wrapper for file_retrieve that searches for highest
    available version first, with no need to retrieve remote-index.

    Keywords:

       relpathnames:  the list of relative pathnames that are being
       searched

       version_list(optional): if the user wants to override the default
       version priority list so this function prioritizes versions
       differently, a different version list can be passed in

     $LastChangedBy: kenb-mac $
     $LastChangedDate: 2007-08-21 08:33:59 -0700 (Tue, 21 Aug 2007) $
     $LastChangedRevision: 1463 $
     $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/file_retrieve_v.pro $

(See ssl_general/misc/file_retrieve_v.pro)

## FILE_SOURCE_DIRNAME

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    Function: file_source_dirname
    Purpose:  Returns the directory path of the source file which calls this function.
       This is useful for determining the directory of associated data files.
    Warning:  May not work for a precompile version of code.
    Author:  D Larson  2008

(See ssl_general/misc/file_source_dirname.pro)

## FILE_TOUCH

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     FILE_TOUCH
     Purpose:  Wrapper routine for the "touch" program that sets file modification and access times
     USAGE:
        file_touch,'foo',systime(1)-300,/mtime   ; sets mod time to 5 minutes ago
     keywords:
        MTIME    set only modification time
        ATIME    set only access time
        VERBOSE  sets VERBOSITY of messages (0: error messages only,  6: lots)
     Restrications:
       Shell executable "touch" must be in path on local operating system.  This is common on unix systems.
       Windows executable available from: http://sourceforge.net/projects/unxutils/
       If the touch executable is not found then no action is taken.
       Test for executable occurs only once.

(See ssl_general/misc/file_touch.pro)

## FIND_CONST_INTERVALS

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    	Procedure: FIND_CONST_INTERVALS

    	Purpose:  Find intervals within the input array where the data are constant to some tollerance,
    		and return the begin and end indices into the original array for those intervals.

    	Calling Sequence:
    		x = [ 1, 1, 3, 3, 4, 1, 1, 1, 1]
    		ctol = 0.01
    		find_const_intervals, x, nint=nint, ibeg=ibeg, iend=iend, ctol=ctol

    	Arguements:
    		X, ARRAY or any type; will be cast to FLOAT for comparison.
    		NINT, LONG, number of intervals of constantcy found in X.
    		IBEG, IEND, LONG[ nint], arrays of array indices to the begin and end of each constant interval.
    		CTOL, FLOAT, tollerance for constancy of data; ABS(dX) lt CTOL for data to be "constant".

    	Notes:
    		None.

     $LastChangedBy: pcruce $
     $LastChangedDate: 2007-06-27 13:16:28 -0700 (Wed, 27 Jun 2007) $
     $LastChangedRevision: 904 $
     $URL $

(See ssl_general/misc/find_const_intervals.pro)

## FIND_STR_ELEMENT

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     **** OBSOLETE!!! Please use "str_element"instead! ***

    FUNCTION:  find_str_element
    PURPOSE:  find an element within a structure
     Input:
       struct,  generic structure
       name,    string  (tag name)
     Purpose:
       Returns index of structure tag.
       Returns -1 if not found
       Returns -2 if struct is not a structure
    KEYWORDS:
      If VALUE is set to a named variable then  the value of that element is
       returned in it.

    CREATED BY:	Davin Larson
    LAST MODIFICATION:	@(#)find_str_element.pro	1.6 95/10/06

(See ssl_general/misc/find_str_element.pro)

## FNAME_TO_TIME

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    PROCEDURE:	fname_to_time, fname, time
    PURPOSE:
    	To translate the name of a standard WIND data file into the starting
    	time of the data.
    INPUT:
    	fname: filename (string) to be translated
    	time: variable in which to return time (double)

    CREATED BY:	Peter Schroeder
    LAST MODIFICATION:	%W% %E%

(See ssl_general/misc/fname_to_time.pro)

## GET_COLORS

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    FUNCTION:    get_colors
    PURPOSE:   returns a structure containing color pixel values
    INPUT:    none
    KEYWORDS:
       NOCOLOR:  forces all colors to !d.table_size-1.

    Written by: Davin Larson    96-01-31
    FILE: get_colors.pro
    VERSION:  1.2
    LAST MODIFICATION: 99/04/07

(See ssl_general/misc/get_colors.pro)

## GET_FILE_NAMES

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    PROCEDURE:  get_file_names,  fnames
    PURPOSE:
       Gets an array of filenames within a time range
    INPUT:
       fnames:  named variable in which the output array of filenames is placed.
    KEYWORDS:
       TIME_RANGE: Two element vector (double or string) specifying the time range.
         If time range is not set, then "GET_TIMESPAN" will be called
         to get a time range.
       MASTERFILE: Use this keyword to pass in one of the following:
    	1) Name of a masterfile that contains times and associated
    	     	filenames.  The file should have the format:
    yyyy-mm-dd/hh:mm:ss   yyyy-mm-dd/hh:mm:ss   fullpathfilename
         		with one line for each file.
    	     (Hint: for CDF files, the masterfile can be created using the
    	     UNIX program 'kpdfile' or the IDL procedure "MAKE_CDF_INDEX".)
    	2) Full path/file names with wildcard characters to search for
    		relevant files.  Input should be in the form:
    		/path/xxx* for files of form /path/xxx_date.
    	3) The name of a previously defined environment variable containing
    		data in the form of 1 or 2 above.
       ROOT_DIR:   Optional root_directory of the masterfile.  This will properly
          manage operating system dependancies.

    CREATED BY:	Davin Larson
    MODIFIED BY:	Peter Schroeder
    VERSION:	1.26 00/10/04 get_file_names.pro

(See ssl_general/misc/get_file_names.pro)

## GET_FILE_NAMES_IND

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    PROCEDURE:  get_file_names_ind,  fnames
    PURPOSE:
       Gets an array of filenames within a masterfile within a time range
    INPUT:
       fnames:  named variable in which the output array of filenames is placed.
    KEYWORDS:
       TIME_RANGE: Two element vector (double or string) specifying the time range.
         If time range is not set, then "GET_TIMESPAN" will be called
         to get a time range.
       MASTERFILE: Name of a masterfile that contains times and associated
         filenames.  The file should have the format:
    yyyy-mm-dd/hh:mm:ss   yyyy-mm-dd/hh:mm:ss   fullpathfilename
         with one line for each file.
         (Hint: for CDF files, the masterfile can be created using the
         UNIX program 'kpdfile' or the IDL procedure "MAKE_CDF_INDEX".)
       ROOT_DIR:   Optional root_directory of the masterfile.  This will properly
          manage operating system dependancies.
       NO_DUPLICATES:  (N;  integer)
          when set the first N characters of file names are compared and only
          the highest version is returned.

    CREATED BY:	Davin Larson
    VERSION:	@(#)get_file_names_ind.pro	1.1 97/06/23

(See ssl_general/misc/get_file_names_ind.pro)

## GET_RT_PATH

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    NAME:
     get_rt_path
    PURPOSE:
      gets the directory of the calling routine.  Used for reliably looking
      up resource paths across platform
    CALLING SEQUENCE:
      get_rt_path,path
    OUTPUT:
      path: the path of the routine that called get_rt_path

    NOTES:
      This is a general version of specific routines like getctpath.
      Eventually those routines should be replaced with this one.

    $LastChangedBy: pcruce $
    $LastChangedDate: 2009-07-16 16:38:39 -0700 (Thu, 16 Jul 2009) $
    $LastChangedRevision: 6439 $
    $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/get_rt_path.pro $

(See ssl_general/misc/get_rt_path.pro)

## GRAD

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    Procedure: Grad

    Purpose:  Calculates the gradient of a 2d or 3d grid in one of two ways.

      In 2d:
      Method1(default):
      gradientX = (grid[x+1,y] - grid[x,y] + grid[x+1,y+1] - grid[x,y+1]) / (2*dx)
      gradientY = (grid[x,y+1] - grid[x,y] + grid[x+1,y+1] - grid[x+1,y]) / (2*dy)

      Method2(leftright):
      gradientX = (grid[x+1,y] - grid[x,y] + grid[x,y] - grid[x-1,y]) / (2*dx)
      gradientY = (grid[x,y+1] - grid[x,y] + grid[x,y] - grid[x,y-1]) / (2*dy)
      This method is actually equivalent to:
      gradientX = (grid[x+1,y] - grid[x-1,y]) / (2*dx)
      gradientY = (grid[x,y+1] - grid[x,y-1]) / (2*dy)

      In 3d:
      Method1(default):
      gradientX = (grid[x+1,y,z] - grid[x,y,z] + grid[x+1,y+1,z] - grid[x,y+1,z] +
                   grid[x+1,y,z+1] - grid[x,y,z+1] + grid[x+1,y+1,z+1] - grid[x,y+1,z+1])
                   / (4*dx)
      gradientY = (grid[x,y+1,z] - grid[x,y,z] + grid[x+1,y+1,z] - grid[x+1,y,z] +
                   grid[x,y+1,z+1] - grid[x,y,z+1] + grid[x+1,y+1,z+1] - grid[x+1,y,z+1])
                   / (4*dy)
      gradientZ = (grid[x,y,z+1] - grid[x,y,z] + grid[x+1,y,z+1] - grid[x+1,y,z] +
                   grid[x,y+1,z+1] - grid[x,y+1,z] + grid[x+1,y+1,z+1] - grid[x+1,y+1,z])
                   / (4*dz)

      Method2(leftright):
      gradientX = grid[x+1,y,z] - grid[x-1,y,z] / (2*dx)
      gradientY = grid[x,y+1,z] - grid[x,y-1,z] / (2*dy)
      gradientZ = grid[x,y,z+1] - grid[x,y,z-1] / (2*dz)

      Method1 will produce an output that is one element smaller in each dimension
      and whose element centers are offset by half the nominal spacing of the grid.

      Method2 will have the same centers and same number of elements as the original
      grid(if the original grid had regular spacing).

    Example:

    Inputs: grid: an NxM grid of points, if it contains NaNs the output may be
                 unpredictable.(or an NxMxP)
            x(optional):  An N length array specifying the positions of the grid points on the x-axis
                 xc should be monotonic and should contain no NaNs.  If unset this routine will
                 assume dx = 1.0
            y(optional):  An M length array specifying the positions of the grid points on the y-axis
                 yc should be monotonic and should contain no NaNs. If unset this routine will
                 assume dy = 1.0
            z:(optional) a P length array specifying the positions of the grid points on
                 the z-axis.  zc should be monotonic and should contain no NaNs. If unset this routine will
                 assume dz = 1.0

    Keywords:
            grad:  The gradient is output through this keyword as an NxMx2 array
            of points.  grad[*,*,0] is the x gradient & grad[*,*,1] is the y gradient

            xout: The positions of the gradient outputs on the x axis are output through this
            keyword as an N length array

            yout: The positions of the gradient outputs on the y axis are output through this
            keyword as an M length array

            xy:  The positions for each output point are passed out as pairs through this
            keyword. The output array will have dimensions N*Mx2,(N times M by 2)

            dxy: The gradient for each point is passed out as pairs through this
            keyword. The output array will have dimensions N*Mx2,(N times M by 2)

            leftright:  Set this keyword if you want to use the second method
            of gradient calculation.

     Notes:
     1. This procedure is not particularly tolerant of NaNs in the input, so
     you should remove them before passing them into this routine.

     2. The output may have slightly different centers/ dimensions as the input.
     This is will definitely be the case if the input array had irregular dimensions.

     3. xy,dxy are useful output format keywords for the plotxyvec routine
     While grad,xout, & yout may be easier for other tasks.

(See ssl_general/misc/grad.pro)

## HIGH_PASS_FILTER

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    NAME:
     high_pass_filter
    PURPOSE:
     subtracts running average from a data array
    CALLING SEQUENCE:
     y = high_pass_filter(array, time_array, no_time_interp=no_time_interp)
    INPUT:
     array = a data array
     time_array = a time array (in units of seconds)
     dt = the averaging time (in seconds)
     no_time_interp = if set, do *not* interpolate the data to the
                      minimum time resolution. The default procedure is
                      to interpolate the data to a regularly spaced grid,
                      and then use ts_smooth to get the running
                      average. This alternative can be slow, but it may
                      save a lot of memory.
     double = if set, do calculation in double precision
                      regardless of input type. (If input data is double
                      calculation is always done in double precision)
     interp_resolution = If time interpolation is being used, set this
                         option to control the number of seconds between
                         interpolated samples.  The default is to use
                         the value of the smallest separation between
                         samples.  Any number higher than this will sacrifice
                         output resolution to save memory. (NOTE: This option
                         will not be applied if no interpolation is being
                         performed because either (1) no_time_interp is set or
                         (2) the sample rate of the data is constant)

     interactive_warning = if keyword is set pops up a message box if there are memory problems and asks
                         the user if they would like to continue
     interactive_varname = set this to a string indicating the name of the quantity to be used in the warning message.

     warning_result = assign a named variable to this keyword to determine the result of the computation
    OUTPUT:
     y = the data array where at each point an average of the data for
     the previous dt has been subtracted.
    HISTORY:
     14-jan-2008, jmm, jimm@ssl.berkeley.edu
     06-feb-2008, teq, teq@ssl.berkeley.edu
     13-mar-2008, jmm, added the default behavior using interpolation
     17-mar-2008, jmm, Gutted and rewritten to use smooth_in_time program
     23-apr-2008, pcruce, Added padding for no_time_interp option, added _extra keyword
     28-apr-2008, pcruce, Added interp_resolution option, added memory warning,
                            mod to guarantee that precision of output is at least as
                            large as precision of input
    $LastChangedBy$
    $LastChangedDate$
    $LastChangedRevision$
    $URL$

(See ssl_general/misc/high_pass_filter.pro)

## HISTBINS

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    FUNCTION:
       H=histbins(R,XBINS)
    Purpose:
       Returns the histogram (H) and bin locations (XBINS) for an array of numbers.
    Examples:
       r = randomn(seed,10000)
       plot,psym=10, xbins, histbins(r,xbins)             ;Use all defaults.
       plot,psym=10, xbins, histbins(r,xbins ,/shift)     ;shift bin edges.
       plot,psym=10, xbins, histbins(r,xbins, binsize=.2)
       plot,psym=10, xbins, histbins(r,xbins, binsize=.2 ,/shift)
       plot,psym=10, xbins, histbins(r,xbins, range=[-10,10])
    NOTE:
       XBINS is an output, not an input!
    Keywords:  (All optional)  Defaults are based on the size and range of input.
       BINSIZE:  Size of bins.
       NBINS: force the output array to have this number of elements. (Use with RANGE)
       RANGE: Limits of histogram
       SHIFT :  Keyword that controls the location of bin edges.
          This has no effect if RANGE is defined.
       NORMALIZE: Set keyword to return a normalized histogram (probability distribution).
       REVERSE:  See REVERSE keyword for histogram
       RETBINS:  If set then an array of bins (same size as r) is returned instead.
    See also: "average_hist", "histbins2d"

(See ssl_general/misc/histbins.pro)

## HISTBINS2D

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    Function:
     h = histbins2d(x,y,xval,yval)
    Input:
       x, y, random variables to bin.
    Output:
       h  number of events within bin
       xval, yval,  center locations of the bins.

(See ssl_general/misc/histbins2d.pro)

## INTERP

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    FUNCTION:   interp(y,x,u)
    PURPOSE:
      Linearly Interpolates vectors with an irregular grid.
      INTERP is functionally the same as INTERPOL, however it is typically
      much faster for most applications.
    USAGE:
      result = interp(y,x,u)
    INPUTS:
           Y:      The input vector can be any type except string.

           X:      The absicissae values for Y.  This vector must have same # of
                   elements as Y.  The values MUST be monotonically ascending
                   or descending.

           U:      The absicissae values for the result.  The result will have
                   the same number of elements as U.  U does not need to be
                   monotonic.
    KEYWORDS:
      NO_CHECK_MONOTONIC:   set this keyword to skip the check for monotonic data.
      INDEX:  Set to named variable to return the index of the closest x less than u.
          (same dimensons as u)
      NO_EXTRAPOLATE:  Set this keyword to prevent extrapolation.
      INTERP_THRESHOLD:  Set to minimum allowed gap size.

    CREATED BY:	Davin Larson  4-30-96
    FILE:  interp.pro
    VERSION:  1.15
    LAST MODIFICATION:  02/04/17

(See ssl_general/misc/interp.pro)

## MAKEGIF

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    PROCEDURE:  makegif, filename
    NAME:
      makegif
    PURPOSE:
      Creates a GIF file from the currently displayed image.
    PARAMETERS:
      filename   filename of gif file to create.  Defaults to 'plot'. Note:
                 extension '.gif' is added automatically
    KEYWORDS:
      ct         Index of color table to load.  Note: will have global
                 consequences!
      multiple   Write multiple gifs to a single file. Subsequent calls to
                 makegif with same filename argument will append to the file.
                 Use /close to close.
      close      close the gif file.  Useful when writing multiple gifs to
                 a single file.  Does not write any image to the file.
      no_expose  Don't print index of current window.

    Restrictions:
      Current device should have readable pixels (ie. 'x' or 'z')

    Created by:  Davin Larson
    FILE:  makegif.pro
    VERSION:  1.11
    LAST MODIFICATION:  02/11/06

(See ssl_general/misc/makegif.pro)

## MAKEJPG

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    PROCEDURE:  makejpg, filename
    NAME:
      makejpg
    PURPOSE:
      Creates a jpg file from the currently displayed image.
    PARAMETERS:
      filename   filename of jpg file to create.  Defaults to 'plot'. Note:
                 extension '.jpg' is added automatically
    KEYWORDS:
      ct         Index of color table to load.  Note: will have global
                 consequences!
      multiple   Does nothing.
      close      Does nothing.
      no_expose  Don't print index of current window.
      mkdir      If set, make the parent directory/directories of the
                 file specified by filename.

    Restrictions:
      Current device should have readable pixels (ie. 'x' or 'z')

    Based almost entirely on makepng by davin larson

    $LastChangedBy: pcruce $
    $LastChangedDate: 2009-11-18 14:36:51 -0800 (Wed, 18 Nov 2009) $
    $LastChangedRevision: 6941 $
    $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/makejpg.pro $

(See ssl_general/misc/makejpg.pro)

## MAKEPNG

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    PROCEDURE:  makepng, filename
    NAME:
      makepng
    PURPOSE:
      Creates a PNG file from the currently displayed image.
    PARAMETERS:
      filename   filename of png file to create.  Defaults to 'plot'. Note:
                 extension '.png' is added automatically
    KEYWORDS:
      ct         Index of color table to load.  Note: will have global
                 consequences!
      multiple   Does nothing.
      close      Does nothing.
      no_expose  Don't print index of current window.
      mkdir      If set, make the parent directory/directories of the
                 file specified by filename.

    Restrictions:
      Current device should have readable pixels (ie. 'x' or 'z')

    Created by:  Davin Larson
    FILE:  makepng.pro
    VERSION:  1.11
    LAST MODIFICATION:  02/11/06

(See ssl_general/misc/makepng.pro)

## MAKEPS.PRO

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    NAME:
     makeps.pro
    PURPOSE:

    OBSOLETE: please use tprint or popen and pclose
     A simple function to reliably and consistently do postscript export
     Right now it will export whatever your last tplot command was(ie
     current plot)
    CALLING SEQUENCE:
     makeps
     -or-
     makeps,'filename'
    INPUT:
     a filename or nothing
    OUTPUT:
     a postscript file to the specified location
     errors, grays out all buttons while processing

    NOTES: Will append a .ps to your filename whether you like it or not
           TODO: add an argument to accept a list of variables

    $LastChangedBy: pcruce $
    $LastChangedDate: 2008-04-14 15:50:24 -0700 (Mon, 14 Apr 2008) $
    $LastChangedRevision: 2719 $
    $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/makeps.pro $

(See ssl_general/misc/makeps.pro)

## MINMAX

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    FUNCTION:   minmax,array
    PURPOSE:  returns a two element array of min, max values
    INPUT:  array
    KEYWORDS:
      MAX_VALUE:  ignore all numbers greater than this value
      MIN_VALUE:  ignore all numbers less than this value
      POSITIVE:   forces MINVALUE to 0

    CREATED BY:    Davin Larson
    LAST MODIFICATION:     @(#)minmax.pro	1.2 02/04/17

(See ssl_general/misc/minmax.pro)

## MK_HTML_HELP2

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     NAME:
    	MK_HTML_HELP2

     PURPOSE:
           Creates a html document from a list of IDL procedures.
    	Given a list of IDL procedure files (.PRO), VMS text library
           files (.TLB), or directories that contain such files, this procedure
           generates a file in the HTML format that contains the documentation
           for those routines that contain a DOC_LIBRARY style documentation
           template.  The output file is compatible with World Wide Web browsers.
           This version is enhanced over the routine supplied by IDL, It will
           also cross reference, print the purpose, and add links to the source
           code.

     CATEGORY:
    	Help, documentation.

     CALLING SEQUENCE:
    	MK_HTML_HELP, Sources, Outfile

     INPUTS:
         Sources:  A string or string array containing the name(s) of the
    		.pro or .tlb files (or the names of directories containing
                   such files) for which help is desired.  If a source file is
                   a VMS text library, it must include the .TLB file extension.
                   If a source file is an IDL procedure, it must include the .PRO
                   file extension.  All other source files are assumed to be
                   directories.  If not provided, searches down directory tree
    		from current directory for files.

         Outfile:	The name of the output file which will be generated without
    		HTML extension.

         If no inputs are given: All directories in the current directory tree
                   are used with the exception of: directories named: 'obsolete'
                   or 'SCCS.'  (UNIX only)

     KEYWORDS:
         TITLE:	If present, a string which supplies the name that
    		should appear as the Document Title for the help.
         FILENAME: Alternative method of specifying Outfile (see above)
         VERBOSE:	Normally, MK_HTML_HELP does its work silently.
    		Setting this keyword to a non-zero value causes the procedure
    		to issue informational messages that indicate what it
    		is currently doing. !QUIET must be 0 for these messages
                   to appear.
         STRICT:   If this keyword is set to a non-zero value, MK_HTML_HELP will
                   adhere strictly to the HTML format by scanning the
                   the document headers for characters that are reserved in
                   HTML (",&,").  These are then converted to the appropriate
                   HTML syntax in the output file. By default, this keyword
                   is set to zero (to allow for faster processing).
         CROSSLINK:If this keyword is set MK_HTML_HELP will create a cross
                   reference between library files.
         CLTURBO:  If this keyword is set to a single character string, then the
                   cross reference procedure will only cross reference lines that
                   contain the character given in CLTURBO.  This greatly increases
                   the speed of the routine.  By default the double quote (") is
                   used
         PRINT_PURPOSE:  If this keyword is set then the first line after PURPOSE:
                   is printed in the output file.
         MASTLIST:	If set, create master list only.  Do not create subdirectory
    		file listings.

     COMMON BLOCKS:
    	None.

     SIDE EFFECTS:
    	A help file with the name given by the Outfile argument is
    	created.

     RESTRICTIONS:
    	The following rules must be followed in formatting the .pro
    	files that are to be searched.
    		(a) The first line of the documentation block contains
    		    only the characters ";+", starting in column 1.
                   (b) There must be a line which contains the string "NAME:",
                       which is immediately followed by a line containing the
                       name of the procedure or function being described in
                       that documentation block.  If this NAME field is not
                       present, the name of the source file will be used.
    		(c) The last line of the documentation block contains
    		    only the characters ";-", starting in column 1.
    		(d) Every other line in the documentation block contains
    		    a ";" in column 1.

           Note that a single .pro file can contain multiple procedures and/or
           functions, each with their own documentation blocks. If it is desired
           to have "invisible" routines in a file, i.e. routines which are only
           for internal use and should not appear in the help file, simply leave
           out the ";+" and ";-" lines in the documentation block for those
           routines.

    	No reformatting of the documentation is done.

     MODIFICATION HISTORY:
           July 5, 1995, DD, RSI. Original version.
           July 13, 1995, Mark Rivers, University of Chicago. Added support for
                   multiple source directories and multiple documentation
                   headers per .pro file.
           July 17, 1995, DD, RSI. Added code to alphabetize the subjects;
                   At the end of each description block in the HTML file,
                   added a reference to the source .pro file.
           July 18, 1995, DD, RSI. Added STRICT keyword to handle angle brackets.
           July 19, 1995, DD, RSI. Updated STRICT to handle & and ".
                   Changed calling sequence to accept .pro filenames, .tlb
                   text librarie names, and/or directory names.
                   Added code to set default subject to name of file if NAME
                   field is not present in the doc header.
           September, 1995, D. Larson. SSL Berkeley. Added crosslink, print_purpose
                   clturbo.
           October 4, 1995, D. Larson. SSL Berkeley. Added link to source file.
           October 3, 1996, F. Marcoline. SSL Berkeley.  Added Alphabet Jumpline.
           October 10, 1996, D. Larson. Added Listing by Directory.
           October 1, 2007, J. McTiernan, allow to work with more than 28
                   directories, dropped obsolete /stream keywords from
                   openw calls.

    FILE:  mk_html_help2.pro
    VERSION 1.26
    LAST MODIFICATION: 99/04/22

(See ssl_general/misc/mk_html_help2.pro)

## NDIMEN

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    FUNCTION: ndimen
    PURPOSE:
      Returns the number of dimensions in an array.
    INPUT:  array
    RETURNS number of dimensions  (0 for scalers,-1 for undefined)

    SEE ALSO:  "dimen", "data_type"

    CREATED BY:	Davin Larson
    LAST MODIFICATION:	@(#)ndimen.pro	1.6 97/03/10

(See ssl_general/misc/ndimen.pro)

## NN

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    NAME:                  nn
    PURPOSE:               Find the index of the data point(s) nearest to the specified time(s)

    CALLING SEQUENCE:      ind=nn(data,time)
    INPUTS:                data:  a data structure, a tplot variable name/index,
                              or a time array
                           time:  (double) seconds from 1970-01-01, scalar or array
                                  if not present, "ctime" is called to get time(s)
    OPTIONAL INPUTS:       none
    KEYWORD PARAMETERS:    x, y, & v:  set to named keywords to return the values
    			of the x, y, & v arrays, if applicable

    OUTPUTS:               a long scalar index or long array of indicies
                           on failure, returns: -2 if bad inputs,
                                                -1 if nearest neighbor not found
    EXAMPLE:               ctime,times,npoints=2
                           inds=nn('Np',times)
                           get_data,'Np',data=dens & get_data,'Tp',data=temp
                           plot,dens.y(inds(0):inds(1)),temp(inds(0):inds(1))
    LAST MODIFICATION:     @(#)nn.pro	1.8 02/04/17
    CREATED BY:            Frank Marcoline

(See ssl_general/misc/nn.pro)

## OPLOT_ERR

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     PROCEDURE:
    	oplot_err, x, low, high
     PURPOSE:
    	Plot error bars over a previously drawn plot.

(See ssl_general/misc/oplot_err.pro)

## PCLOSE

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    PROCEDURE:   pclose
    INPUT:  none
    PURPOSE: Close postscript file opened with popen, and change device back to
      default.
      If common block string 'printer_name' is set, then file is sent to that
      printer.
    SEE ALSO: 	"print_options"
    		"popen"

    CREATED BY:	Davin Larson
    LAST MODIFICATION:	@(#)pclose.pro	1.10 99/02/18

(See ssl_general/misc/pclose.pro)

## PLOT_POSITIONS

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    FUNCTION:   plot_positions
    PURPOSE:
      Procedure that will compute plot positions for multiple plots per page.
    Created by Davin Larson

(See ssl_general/misc/plot_positions.pro)

## POPEN

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    PROCEDURE: popen, filename
    PURPOSE:
      Change plot device to postscript.
    INPUT:    optional;  if:
      string   :  string used as filename,  '.ps' extension is added automatically
      integer X:  filename set to 'plotX.ps'.  value of x is incremented by 1.
      none:       filename set to 'plot.ps'
    KEYWORDS: See print_options for info.
      COPY:    pass COPY keyword to set_plot
      INTERP:  pass INTERP keyword to set_plot  (default is to have interp off)
      XSIZE:   postscript plot size in the x direction
      YSIZE:   postscript plot size in the y direction
      UNITS:   plot size units (inches or cm)
    SEE ALSO:	"pclose",
    		"print_options",
    		"popen_com"
    HISOTRY:
     4-apr-2008   cg, added optional keywords for postscript plot size
                      units for plot size variables
    CREATED BY:	Davin Larson
    LAST MODIFICATION:	@(#)popen.pro	1.21 98/06/23

(See ssl_general/misc/popen.pro)

## POPEN_COM

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    COMMON BLOCK:	popen_com
    PURPOSE:	Common block for print routines

    SEE ALSO:	"popen","pclose",
    		"print_options"

    CREATED BY:	Davin Larson
    LAST MODIFICATION:	@(#)popen_com.pro	1.10 97/12/05

(See ssl_general/misc/popen_com.pro)

## PRINTDAT

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    PROCEDURE: printdat,[x]
    PURPOSE:
       Displays information and contents of a data variable. (Very similar to HELP procedure but much more verbose.)
       This routine is most useful for displaying contents of complex
       data structures.
       If printdat is called without arguments then information on all variables
       within the calling routine are displayed.
       POINTER occurences are recursively displayed as well. (only non-null pointers are listed)

    Keywords:
       FULL     Set this keyword to display full variable output.
       NAMES = string:  Optional list of variables to display (Same as for HELP)
       WIDTH:   Width of screen (Default is 120).
       MAX:     Maximum number of array elements to print.  (default is 30)
       NSTRMAX  Maximum number of structure elements to print. (default is 3)
       NPTRMAX  Maximum number of structure elements to print. (default is 5)
       OUTPUT=string :  named variable in which the output is dumped.
       VARNAME=string : [optional] name of variable to be displayed. (useful if input is an expression instead of a variable)
       RECURSEMAX = integer :  Maximum number of levels to dive into. (Useful for limiting the output for heavily nested structures or pointers)

    Written by Davin Larson, May 1997.

     $LastChangedBy: davin-win $
     $LastChangedDate: 2008-02-29 11:40:28 -0800 (Fri, 29 Feb 2008) $
     $LastChangedRevision: 2431 $
     $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/printdat.pro $

(See ssl_general/misc/printdat.pro)

## PRINT_OPTIONS

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    PROCEDURE: print_options

    PURPOSE:  controls postscript printing options

    KEYWORDS:

      PORT:   print pages in portrait format (default)

      LAND:   print pages in landscape format

      BW:     Use black and white mode  (untested)

      COLOR:  Use Color postscript (default)

      XSIZE:  plot size dimension in the x direction

      YSIZE:  plot size dimension in the y direction

      UNITS:  plot size units (inches or cm)

    FUTURE OPTIONS:

      Ecapsulated postscript format

      changing plotting area

    HISOTRY:

     4-apr-2008   cg, added optional keywords for postscript

                      file size and file size units

    SEE ALSO:	"popen","pclose"

    CREATED BY:	Davin Larson

    LAST MODIFICATION:	@(#)print_options.pro	1.16 97/05/30

(See ssl_general/misc/print_options.pro)

## PTRACE

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    FUNCTION: PTRACE()
    PURPOSE: Returns a string that provides the current program location.
    KEYWORDS:
        OPTION:  The value of the option is retained in a common block
               OPTION=0  : returns null string
               OPTION=1  : returns highest level routine name.
               OPTION=2  : returns highest level routine name (indented).
               OPTION=3  : returns all levels

    Usage: Generally useful for debugging code and following code execution.
    Example:
      if keyword_set(verbose) then  print,ptrace(),'X=',x

    Written:  Jan 2007,  D. Larson

(See ssl_general/misc/ptrace.pro)

## PTR_EXTRACT

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    NAME: ptr_extract
    Function: ptrs = ptr_extract(p,EXCEPT=EXCEPT)
    Purpose:
       Recursively searches the input (of any type) and returns an array of all
       pointers found.
       This is useful for freeing pointers contained within some complicated
       structure heirachy or pointer list.
       if no pointers are found then a scaler null pointer is returned.
       This routine ignores object pointers!
    Keywords:
       EXCEPTPTRS = an array of pointers that should not be included in the output.
    Created by Davin Larson. May 2002.

(See ssl_general/misc/ptr_extract.pro)

## PWRSPC

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    NAME:
     pwrspc
    PURPOSE:
        Called with times time and data quantity, PWRSPC returns a power
        spectrum power at frequencies freq. A Hanning window is applied to
        the input data, and its power is divided out of the returned
        spectrum. A straight line is subtracted from the data to
        reduce spurius power due to sawtooth behavior of a background.
        UNITS ARE (UNITS)^2 WHERE UNITS ARE THE UNITS OF quantity. freq
        is in 1/timeunits.
        THUS THE OUTPUT REPRESENTS THE MEAN SQUARED AMPLITUDE OF THE SIGNAL
           AT EACH SPECIFIC FREQUENCY. THE TOTAL (SUM) POWER UNDER THE CURVE IS
           EQUAL TO THE MEAN (OVER TIME) POWER OF THE OSCILLATION IN TIME DOMAIN.
        NOTE: IF KEYWORD notperhz IS SET, THEN POWER IS IN UNITS^2. If notset
               power is (as normal) in UNITS^2/Hz.
    CALLING SEQUENCE:
     pwrspc, time, quantity, freq, power, noline = noline, $
             nohanning = nohanning, bin = bin, notperhz = notperhz
    INPUT:
     time = the time array
     quantity = the function for which you want to obtain a power
                spectrum
    OUTPUT:
     freq = the frequency array (units =1/time units)
     power = the power spectrum, (units of quantity)^2/frequency_units
    KEYWORDS:
     noline = if set, no straight line is subtracted
     nohanning = if set, then no hanning window is applied to the input
     bin = a binsize for binning of the data, the default is 3
     notperhz = if set, the output units are simply the square of the
                input units
     err_msg = named variable that contains any error message that might occur

    $LastChangedBy$
    $LastChangedDate$
    $LastChangedRevision$
    $URL$

(See ssl_general/misc/pwrspc.pro)

## SETBP

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    PROCEDURE:  setbp, module
        This procedure will set BREAKPOINTS at all lines within a program module
        file that contain the string:  ";bp"
        A conditional break point is set with  ;bpif  condition statement

    Input:  module (string)
    Purpose:   This is a DEBUGGING tool that is used to set breakpoints.
    Keywords:
        /FUNCTION  Set this keyword if module is a function.

     Author:  Davin Larson 2007

(See ssl_general/misc/setbp.pro)

## SHARE_COLORS

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    PROCEDURE:
      share_colors
    PURPOSE:
      Procedure that allows multiple IDL sessions to share the same color table.
      The procedure should be called in each session before any
      windows are created.
    USAGE:
      Typically this procedure will be put in a startup routine. such as:
      share_colors,first=f
      if f then loadct,39

    KEYWORDS:
      FIRST Named variable that will be set to 1 if this is the
          first session, and set to 0 otherwise.
    SIDE EFFECTS:
      Creates a temporary file with the name 'idl_cmap:NAME' on the users home
      directory where NAME is the name of the display machine.
      This file is deleted upon exiting IDL.
      The procedure is only useful on UNIX for users with a common home directory.

(See ssl_general/misc/share_colors.pro)

## SMOOTH_IN_TIME

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    NAME:
     smooth_in_time
    PURPOSE:
     Runs smooth for irregular grids, after regularising grid
    CALLING SEQUENCE:
     ts = smooth_in_time(array, time_array, dt, /backward, /forward,
                      /double, /no_time_interp)
    INPUT:
     array = a data array, can be 2-d (ntimes, n_something_else), the
             first index is smoothed or averaged.
     time_array = a time array (in units of seconds)
     dt = the averaging time (in seconds)
    KEYWORDS:
     backward = if set, perform an average over the previous dt, the
                default is to average from t-dt/2 to t_dt/2
     forward = if set, perform an average over the next dt
     double = if set, do calculation in double precision
                      regardless of input type. (If input data is double
                      calculation is always done in double precision)
     no_time_interp = if set, do *not* interpolate the data to the
                      minimum time resolution. The default procedure is
                      to interpolate the data to a regularly spaced grid,
                      and then use ts_smooth to get the running
                      average. This alternative can be slow.
     smooth_nans = if set, replace Nan values in the input array with the
                   average values calculated using the ts_smooth
                   process. This has not been implemented for the
                   no_time_interp option.
     true_t_integration = if set, subtract 1/2 of the end points of the
                          integration from each value, to obtain the
                          value for an integration over time of the
                          appropriate interval. This has not been
                          implemented for the no_time_interp option.
                          Ths is created for the high_pass_filter.
     interp_resolution = If time interpolation is being used, set this
                         option to control the number of seconds between
                         interpolated samples.  The default is to use
                         the value of the smallest separation between
                         samples.  Any number higher than this will sacrifice
                         output resolution to save memory. (NOTE: This option
                         will not be applied if no interpolation is being
                         performed because either (1) no_time_interp is set or
                         (2) the sample rate of the data is constant)
     dtx_min_fraction = When interp_resolution is not set, the default is to use
                        the value of the smallest separation between
                        samples, with the caveat that this value of smallest
                        separation has to occur relatively
                        frequently. Dtx_min_fraction is used to get an
                        effective value for the minimum of the input time
                        resolution. If a suspected minimum value occurs
                        less than dtx_min_fraction times the peak of a
                        histogram of time resolutions, it is
                        discarded. The default value is 0.10
     interactive_warning = if keyword is set pops up a message box if there are memory problems and asks
                         the user if they would like to continue

     interactive_varname = set this to a string indicating the name of the quantity to be used in the warning message.

     warning_result = assign a named variable to this keyword to determine the result of the computation
    OUTPUT:
     ts = the data array smoothed or averaged
    HISTORY:
     13-mar-2008, jmm, jimm@ssl.berkeley.edu, hacked from
     high_pass_filter.pro and added ts_smooth as the default
     13-mar-2008, ts_smooth is way too slow, just uses smooth.pro now
     6-may-2008, jmm, added sort for input data for cases with
                      non-monotonic time_arrays
     23-apr-2008, pcruce, Added padding for no_time_interp option, added _extra keyword
     28-apr-2008, pcruce, Added interp_resolution option, added memory warning,
                            mod to guarantee that precision of output is at least as
                            large as precision of input
    $LastChangedBy: jimm $
    $LastChangedDate: 2009-10-27 15:47:46 -0700 (Tue, 27 Oct 2009) $
    $LastChangedRevision: 6899 $
    $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/smooth_in_time.pro $

(See ssl_general/misc/smooth_in_time.pro)

## SPACE_BAR

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      Procedure: space_bar

      Purpose: generates a horizontal bar stored in a tplot variable
               that is used to adjust the spacing between tplot variables
               in plots

      Arguments:
                 n(positional,required): a double representing the height
                 of the space bar

                 newname(keyword,optional): the name you want the bar to
                 have(default: 'space_bar')

     $LastChangedBy: pcruce $
     $LastChangedDate: 2008-01-17 14:37:52 -0800 (Thu, 17 Jan 2008) $
     $LastChangedRevision: 2286 $
     $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/tplot/tplotxy.pro $

(See ssl_general/misc/space_bar.pro)

## SSL_CORRELATE_TPLOT

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     NAME:
          ssl_correlate_tplot

     PURPOSE:
            Identified the amount of shift required to correlate two
            time series tplot variables and stores the result in a tplot
            variable. Only compares 1-d to 1-d data at a time So for example you
            can, compare the fge x and the fgl_x but can't do all three
            at a time.

          Works by binning the timeseries data, then calculating the
          time shift required to maximally correlate each bin.
          When too few points overlap bins are rejected.

     CATEGORY:
           THEMIS-SOC

     CALLING SEQUENCE:
          pro thm_correlate_tplot,var1_name, var1_y_dim, var2_name, var2_y_dim, store_name, correlation_floor = correlation_floor, point_number =  point_number, lag_step_number = lag_step_number, time_step_size = time_step_size, bin_size = bin_size

     INPUTS:

           var1_name: the tplot name of the first variable to be compared

           var1_y_dim: the numerical dimension of the first tplot y_var to look
           at(from 0 to n-1)

           var2_name: the tplot name of the second variable to be
           compared

           var2_y_dim: the numerical dimension of the second tplot y_var
           to look at(from 0 to n-1)

           store_name: the name of a tplot variable in which to store the result

           correlation_floor: optional, if set filters all results where
           the correlation between functions is too poor(default:.9)

           point_number: optional, the minimum number of points of
           overlap necessary to try correlating a bin(default:200)

           lag_step_number: optional, checks plus or minus lag_steps * time steps
           to correlate the vectors (default:64)

           time_step_size: optional, the size of the time step to use when
           interpolating and correlating the vectors, in
           seconds(default:1/128 seconds)

           bin_size: optional, the size of each bin in seconds
           (default:60 seconds)

     OUTPUTS:

           stores the time and the shift values in the select tplot_var

     KEYWORDS:

     COMMENTS: This function will probably die horribly if time
      values are not monotonic.

     PROCEDURE:

     EXAMPLE:

     MODIFICATION HISTORY:
           Written by: Patrick Cruce(pcruce@gmail.com)
           2007-05-24        V1.0

    ;$LastChangedBy: pcruce $
    $LastChangedDate: 2007-08-17 11:32:29 -0700 (Fri, 17 Aug 2007) $
    $LastChangedRevision: 1439 $
    $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/ssl_correlate_tplot.pro $

     KNOWN BUGS:

(See ssl_general/misc/ssl_correlate_tplot.pro)

## SSL_CORRELATION_SHIFT

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     NAME:
          ssl_correlation_shift

     PURPOSE:
          Calculates the shift required to correlate two tme series of
          data.  Does this by binning the timeseries data, then
          calculating the time shift required to maximally correlate each
          bin.  When too few points overlap bins are rejected.

     CATEGORY:
           THEMIS-SOC

     CALLING SEQUENCE:
           lag_time_series = thm_correlation_shift(var1_time_series,var2_time_series)

     INPUTS:

           var1_time_series: a 2xn matrix(column major) of n time/value pairs for var1

           var2_time_series: a 2xn matrix(column major) of n time/value pairs for var2

           n_pts: optional, the minimum number of points of overlap necessary to
           try correlating a bin

           lag_steps: optional, checks plus or minus lag_steps * time steps
           to correlate the vectors

           time_step: optional, the size of the time step to use when
           interpolating and correlating the vectors

           bin_size: optional, the size of each bin in seconds

     OUTPUTS:

           an 3xn matrix(column major) of time/shift/correlation triplets
           or -1L on failure,
           the output n is the number of bins constructed

     KEYWORDS:

     COMMENTS: This function will probably die horribly if time
      values are not monotonic.

     PROCEDURE:

     EXAMPLE:

     MODIFICATION HISTORY:
           Written by:       Jim Lewis
           2007-04-19        Initial version
           Updated by: Patrick Cruce(pcruce@gmail.com)
           2007-05-22        V2.0

    $LastChangedBy: pcruce $
    $LastChangedDate: 2007-08-17 11:32:29 -0700 (Fri, 17 Aug 2007) $
    $LastChangedRevision: 1439 $
    $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/ssl_correlation_shift.pro $

(See ssl_general/misc/ssl_correlation_shift.pro)

## SSL_SET_COMPLEMENT

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    Purpose: Calculates the complement of l2 - l1
              (ie set difference)

    Arguments: l1 subset,l2 superset

    Notes: empty set is -1L
           all inputs must be empty set or arrays
           all outputs will be empty set or arrays
           Arrays must be of homogenous type

(See ssl_general/misc/ssl_set_complement.pro)

## SSL_SET_INTERSECTION

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    Purpose: Performs an intersection of two sets
    Parameters: l1,l2 sets(arrays) for which the intersection is
    calculated

    Returns: -1L on empty set, otherwise intersection of the two sets

    Notes: empty set is -1L
           all inputs must be empty set or arrays
           all outputs will be empty set or arrays
           Arrays must be of homogenous type

(See ssl_general/misc/ssl_set_intersection.pro)

## SSL_SET_UNION

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    FUNCTION ssl_set_union(set1,set2)

    Purpose: returns the union of two sets

    Notes: empty set is -1L
           all inputs must be empty set or arrays
           all outputs will be empty set or arrays
           Arrays must be of homogenous type

(See ssl_general/misc/ssl_set_union.pro)

## SSL_TIME_CHECK

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    PROCEDURE:     ssl_time_check.pro
    PURPOSE:   prints information about gaps between timestamps in cdf files
    INPUT:
       dir: The directory in which to search for cdfs
       out: the output directory for the limit files
       LIM: reassign the limit if you want it is a 2 element array
       MNEM: optional regex to filter timestamp mnems
    KEYWORDS:
       none

    COMMENTS: Will check all timestamps for all cdfs in the directory and
    output a seperate file for each type of timestamp.
    File format is:
    timestamp1 timestamp2 gap_size record_number

    currently it signals a gap if a gap is over 180 seconds or negative

    EXAMPLE: thm_time_check,'/','/dev/null'

    CREATED BY:    Patrick Cruce (pcruce@gmail.com)

    $LastChangedBy: pcruce $
    $LastChangedDate: 2007-08-17 11:32:29 -0700 (Fri, 17 Aug 2007) $
    $LastChangedRevision: 1439 $
    $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/ssl_time_check.pro $

(See ssl_general/misc/ssl_time_check.pro)

## STR2TIME

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    FUNCTION str2time(string, informat=string)
     INPUT: scaler string.
     Returns seconds since 1970 given virtually any input string.
     (Assumes the string is GMT)
     The user should specify the input order of Year, Month, Date, hour, min, second is with INFORMAT keyword
     INFORMAT should be a 6 character string:  "YMDhms"  specifies Year/Mon/Date-hour:minute:second
     examples:      time = str2time(systime(),informat='MDhmsY')
                    time = str2time('tue, 04 jul 2006 19:00:04 gmt',informat='DMYhms')
     Written by Davin Larson - 2007

(See ssl_general/misc/str2time.pro)

## STRFILTER

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    FUNCTION:
      res =  strfilter(stringarray,searchstring)
    PURPOSE:
      Returns the subset of stringarray that matchs searchstring
      '*' will match all (non-null) strings
      ''  will match only the null string
      Output can be modified with keywords
      NOTE: this routine is very similar to the STRMATCH routine introduced in IDL 5.3
         it has some enhancements that make it useful.
         (i.e.: filterstring can also be an array)
    INPUT:
      stringarray:  An array of strings to be filtered
      searchstring: A string that may contain wildcard characters ("*")
               (If searchstring is an array then results are OR'd together)
    RETURN VALUE:
      Either:
         Array of matching strings.
      or:
         Array of string indices.
      or:
         Byte array with same dimension as input string.
      Depends upon keyword setting (See below)

    KEYWORDS:
      FOLD_CASE: if set then CASE is ignored.   (only IDL 5.3 and later)
      STRING: if set then the matching strings are returned.  (default)
      INDEX:  if set then the indices are returned.
      BYTES:  if set then a byte array is returned with same dimension as input string array (similar to STRMATCH).
      NEGATE: pass only strings that do NOT match.
      COUNT:  A named variable that will contain the number of matched strings.
    Limitations:
      This function still needs modification to accept the '?' character
      July 2000;  modified to use the IDL strmatch function so that '?' is accepted for versions > 5.4
    EXAMPLE:
      Print,strfilter(findfile('*'),'*.pro',/negate) ; print all files that do NOT end in .pro
    AUTHOR:
      Davin Larson,  Space Sciences Lab, Berkeley; Feb, 1999
    VERSION:  01/10/08

(See ssl_general/misc/strfilter.pro)

## STRING_PARSER

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    NAME:
           string_parser
    PURPOSE:
           Parse strings into components
    CALLING SEQUENCE:
           string_parser, inpx, parse_by, out, output_count
    INPUT:
           inpx     strings to parse
           parse_by        character to parse by
    OUTPUT:
           out     array of substrings
           output_count    number of substrings
    HISTORY:
           Updated 22-April-1993 by Terry Slocum
           Fixed output_count bug, 28-mar-94, JMM
           Gave the ability to use a parse_by string of more than one
           character, jmm 13-jun-2007

(See ssl_general/misc/tuserdef.pro)

## STRIPPATH

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     FUNCTION:
            STRIPPATH

     DESCRIPTION:

           Function that strips off any directory components from a full
           file path, and returns the file name and directory components
           seperately in the structure:
                   {file_cmp_str,file_name:'file',dir_name:'dir'}
           This is only implemented for UNIX at this time.

     USAGE (SAMPLE CODE FRAGMENT):

       ; find file component of /usr/lib/sendmail.cf
           stripped_file = STRIPPATH('/usr/lib/sendmail.cf')

      The variable stripped_file would contain:

           stripped_file.file_name = 'sendmail.cf'
           stripped_file.dir_name  = '/usr/lib/'

     REVISION HISTORY:

       $LastChangedBy: kenb-mac $
       $LastChangedDate: 2006-12-15 08:13:48 -0800 (Fri, 15 Dec 2006) $
       $LastChangedRevision: 97 $
       $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/strippath.pro $
           Originally written by Jonathan M. Loran,  University of
           California at Berkeley, Space Sciences Lab.   Oct. '92
       Updated to use IDL 6.0 features for cross-platform usability.

(See ssl_general/misc/strippath.pro)

## STRUCT_VALUE

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    FUNCTION: struct_value(struc,name,default=default,index=index)
    PURPOSE:  Returns the value of a structure element.
       Function equivalent to the procedure: "STR_ELEMENT"
       if "name" is an array then a new structure is returned with only the named values.
    Author:  Davin Larson, 2006

(See ssl_general/misc/struct_value.pro)

## STR_ELEMENT

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    PROCEDURE:  str_element, struct,  tagname, value
    PURPOSE:
     Find (or add) an element of a structure.
     This procedure will not
     Input:
       struct,  generic structure
       tagname,    string  (tag name)
     Output:
       value,  Named variable in which value of the structure element is returned.
     Purpose:
       Retrieves the value of a structure element.  This function will not produce
       an error if the tag and/or structure does not exist.
    KEYWORDS:
      SUCCESS:  Named variable that will contain a 1 if the element was found
         or a 0 if not found.
      INDEX: a named variable in which the element index is returned.  The index
         will be -2 if struct is not a structure,  -1 if the tag is not found,
         and >= 0 if successful.
      ADD_REPLACE:  Set this keyword to add or replace a structure element.
      DELETE:   Set this keyword to delete the tagname.
      CLOSEST:  Set this keyword to allow near matchs (useful with _extra)
      VALUE: (obsolete) alternate method of returning value. (Will not work with recursion)
    Notes:
      1. Value remains unchanged if the structure element does not exist.
      2. If tagname contains a '.' then the structure is recursively searched and
           index will be an array of indices.
      3. If struct is an array then results may be unpredictable.
      4. Elements may be inserted into embedded structures, by including the
           embedded structure name in the tagname string.(example below)

    Examples:
        Does an element exist?
        str_element,my_str,'my_tag_name',SUCCESS=s
        What is an element's value?
        str_element,my_str,'my_tag_name',v
        Add an element
        str_element,my_str,'my_tag_name','value',/add
        Add an element to embedded structure:
        str_element,my_str,'my_substr_name.my_tag_name','value',/add

    Modifications:
      5/7/97: Added recursive searching of structure hierarchy.  D. Larson

    CREATED BY:    Davin Larson
    FILE:  str_element.pro
    VERSION  1.10
    LAST MODIFICATION: 01/10/08

(See ssl_general/misc/str_element.pro)

## TAG_NAMES_R

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     FUNCTION:  TAG_NAMES_R(STRUCTURE, [TYPE=dt] )
     PURPOSE:  Very similar to the TAG_NAMES function but recursively
               obtains all structure names within imbedded structures as well.
     INPUT: STRUCTURE: A structure typically.
                  If input is not a structure then a null string is returned
     KEYWORDS:
           TYPE=var; Named variable in which to return and array of data types.
     RETURNS:  Returns an array of strings

(See ssl_general/misc/tag_names_r.pro)

## TCLIP

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    NAME:
     tclip
    PURPOSE:
     wapper for xclip.pro allowing input of tplot variable names
    CALLING SEQUENCE:
     tclip, varnames, amin, amax, _extra=_extra
    INPUT:
     varnames = an array (or scalar) of tplot variable names
     amin, amax = the minumum and maximum values
    KEYWORDS:
     flag = the value that clipped data are  set to, the default is
            -0.0/0.0 (NaN)
     newname = if set,give these names to the clipped data, the
                    default is to append '_clip' to the input names and
                    pass out the names in the newname variables,
                    Unless /overwrite is set. This will not work for wild
                    card input.
     overwrite = if set, write the new data back to the old tplot
                 variables, do not set this with newname
    HISTORY:
     2-feb-2007, jmm, jimm.ssl.berkeley.edu

    $LastChangedBy$
    $LastChangedDate$
    $LastChangedRevision$
    $URL$

(See ssl_general/misc/tclip.pro)

## TDEFLAG

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    NAME:
     tdeflag
    PURPOSE:
     wapper for xdeflag.pro allowing input of tplot variable names
    CALLING SEQUENCE:
     tdeflag, varnames, method, newname=newname, $
              overwrite = overwrite, _extra=_extra
    INPUT:
     varnames = an array (or scalar) of tplot variable names
     method = set to "repeat", this will repeat the last good value.
              set to "linear", then linear interpolation is used, but for
              the edges, the closest value is used, there is no
              extrapolation
    KEYWORDS:
     flag = all values greater than 0.98 times this value will be deflagged,
            the default is 6.8792e28, Nan's, Inf's are also deflagged
     maxgap = the maximum number of rows that can be filled? the default
               is n_elements(t)
     newname = if set,give these names to the deflagged data, the
                    default is to append '_deflag' to the input names and
                    pass out the names in the newname variables,
                    Unless /overwrite is set
     overwrite = if set, write the new data back to the old tplot
                 variables, do not set this with newname
    HISTORY:
     2-feb-2007, jmm, jimm.ssl.berkeley.edu

    $LastChangedBy$
    $LastChangedDate$
    $LastChangedRevision$
    $URL$

(See ssl_general/misc/tdeflag.pro)

## TDEGAP

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    NAME:
     tdegap
    PURPOSE:
     wrapper for xdegap.pro allowing input of tplot variable names
    CALLING SEQUENCE:
     tdegap, varnames, dt=dt, margin=margin, maxgap=maxgap,$
             newname=newname, overwrite=overwrite
    INPUT:
     varnames = an array (or scalar) of tplot variable names
    KEYWORDS:
     dt = the nominal time resolution of the data that will be inserted,
          the default is to choose the median of the input time array
     margin = the margin used to determine if a gap is big enough, the
              default is 0.25 seconds
     maxgap = the maximum gap size that will be allowed to be filled, in
              units of dt. the default is to set this to the max number
              of data points
              (TDEGAP degaps anything that is greater than dt+margin
              and less than maxgap*dt)
     newname = if set,give these names to the degapped data, the
                    default is to append '_degap' to the input names and
                    pass out the names in the newname variables,
                    Unless /overwrite is set
     overwrite = if set, write the new data back to the old tplot
                 variables, do not set this with newname
     (Keywords passed to XDEGAP:)
     nowarning = if set, suppresses warnings
     flag = A numeric user-specified value to use for flagging gaps.
       Defaults to a floating NaN.  If an array is entered, only the
       first element is considered.If a non-numeric datatype is entered,
       its value is ignored.
     onenanpergap = Fill gaps with only one NaN -> useful for conserving memory.
       Also, for reference concerning post-processing, the INTERPOL function
       propagates a single NaN just as it would many NaNs.
    HISTORY:
     9-apr-2007, jmm, jimm.ssl.berkeley.edu
     10-oct-2008, jmm, Degaps v tags if necessary

    $LastChangedBy$
    $LastChangedDate$
    $LastChangedRevision$
    $URL$

(See ssl_general/misc/tdegap.pro)

## TDESPIKE_AE

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           Name: TDESPIKE_AE

           Purpose:  This routine removes artificial spikes. Note that it is
                     ONLY meant to be used for the calculation of the
                     'THEMIS AE index' in the overview plots.

           Variable:  lower = lower cutoff of spikes to be removed
                      upper = upper cutoff of spikes to be removed

           Keywords:  none

           Example:   tdespike_AE, -2000.0, 1500.0

           Notes:     Written by Andreas Keiling, 29 August 2007

     $LastChangedBy: aaflores $
     $LastChangedDate: 2009-08-03 10:43:14 -0700 (Mon, 03 Aug 2009) $
     $LastChangedRevision: 6516 $
     $URL $

(See ssl_general/misc/tdespike_ae.pro)

## TDPWRSPC

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    NAME:
     tdpwrspc
    PURPOSE:
     wapper for dpwrspc.pro allowing input of a tplot variable name
    CALLING SEQUENCE:
     tdpwrspc, varname, newname=newname,_extra=_extra
    INPUT:
     varname = one tplot variable name
    KEYWORDS:
     newname = if set,give this name to the new data, the
               default is to append '_dpwrspc' to the input name and
               pass out the name in the newname variable,
               Unless /overwrite is set
     overwrite = if set, write the new data back to the old tplot
                 variable, do not set this with newname

     nboxpoints = the number of points to use for the hanning window, the
                  default is the closest power of 2 less than the number of points divided by 32
     nshiftpoints = the number of points to shift the hanning window per-step, the default in nboxpoints/2

     bin = a binsize for binning of the data along the frequency domain, the default is 3
     tbegin = a start time, the default is time[0]
     tend = an end time, the default is time[n_elements(time)-1]
     noline = if set, no straight line is subtracted
     nohanning = if set, then no hanning window is applied to the input
     notperhz = if set, the output units are simply the square of the
                input units
    HISTORY:
     27-mar-2007, jmm, jimm.ssl.berkeley.edu
     10-apr-2007, jmm, fixed 2 bugs wrt structure definition

    $LastChangedBy$
    $LastChangedDate$
    $LastChangedRevision$
    $URL$

(See ssl_general/misc/tdpwrspc.pro)

## THIGH_PASS_FILTER

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    PROCEDURE: thigh_pass_filter, varname, dt, newname = newname
    PURPOSE:
     Uses high_pass_filter to calculate a running average of the input data and
       store the data with the running average subtracted in an output tplot variable.

    INPUT:
     varname = variable passed to get_data, example - thg_mag_ccnv
     dt = the averaging time (in seconds)
    KEYWORDS:
     newname: set output variable name
     no_time_interp:  Set to save memory by preventing interpolation of time
                      array when smoothing data before subtraction.
                      This option will probably be significantly slower.
     double:  Set so operation is performed at double precision
                      regardless of input type. (If input data is double
                      calculation is always done in double precision)
     interp_resolution = If time interpolation is being used, set this
                         option to control the number of seconds between
                         interpolated samples.  The default is to use
                         the value of the smallest separation between
                         samples.  Any number higher than this will sacrifice
                         output resolution to save memory. (NOTE: This option
                         will not be applied if no interpolation is being
                         performed because either (1) no_time_interp is set or
                         (2) the sample rate of the data is constant)

     interactive_warning = pops up a message box if there are memory problems and asks
                         the user if they would like to continue

     warning_result = assign a named variable to this keyword to determine the result of the computation

    HISTORY:
     14-jan-2008, jmm, jimm@ssl.berkeley.edu
     06-feb-2008, teq, teq@ssl.berkeley.edu
     23-Apr-2009, pcruce, pcruce@igpp.ucla.edu, Added extra keyword support
     28-apr-2008, pcruce, Added interp_resolution option, added memory warning,
                            mod to guarantee that precision of output is at least as
                            large as precision of input
    $LastChangedBy$
    $LastChangedDate$
    $LastChangedRevision$
    $URL$

(See ssl_general/misc/thigh_pass_filter.pro)

## TIME_AVERAGE

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     Function: time_average

     Calculates a bin based average over time series data
     Uses a histogram internally so it should be pretty quick

     Arguments:
           time: the time array for the input timeseries
           data: the data array for the input timeseries
           newtime(optional): named variable in which to return the times
                  for each bin upon which an average is calculated
           trange(optional): a time range over which the average is
           performed
           resolution(optional): the size of each bin in seconds
           ret_total(optional): named variable in which totals for each
           bin are returned
           ret_min(optional): named variable in which mins for each bin
           are returned
           ret_med(optional): named variable in which medians for each
           bin are returned

     $LastChangedBy: pcruce $
     $LastChangedDate: 2007-11-01 15:32:37 -0700 (Thu, 01 Nov 2007) $
     $LastChangedRevision: 1911 $
     $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/time_average.pro $

(See ssl_general/misc/time_average.pro)

## TIME_CLIP

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    Procedure: time_clip

    Purpose: clips a tplot variable between a start time and an end time

    Inputs:   tplot_var_name: the name of the variable to be clipped

              start_time: the start time for the clipping(double or string)

              end_time: the end time for the clipping(double or string)

    Keywords:
              newname(optional): the name of the output tplot variable
                       otherwise it will be tplot_var_name+'_tclip'

              tvar(optional): set this keyword and start_time and
              end_time will be interpreted as the names of tplot variables
              The start and end times will then be taken from the first
              and last component of the tplot variables listed

              replace(optional): set this to replace the variable,  rather than create
              a new one

              error(optional): set this to a named variable to return the
              error status of the function, it will return 0 for no error
              and 1 to signal an error.  This may be set to true even if
              the error was non fatal.  Also if you are using globbing
              to modify many tplot variables it will signal an error if
              any of the variables failed

              examples:
                     time_clip,'thb_fgs_gsm','2007-03-23/10:00:00','2007-03-23/12:00:00',newname='thb_fgs_gsm_10t12clip'
                     time_clip,'thb_peem_velocity','thb_fgs_gsm',thb_fgs_gsm',/tvar

     $LastChangedBy: pcruce $
     $LastChangedDate: 2008-01-03 13:53:59 -0800 (Thu, 03 Jan 2008) $
     $LastChangedRevision: 2224 $
     $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/idl_socware/trunk/external/IDL_GEOPACK/trace/ttrace_crib.pro $

(See ssl_general/misc/time_clip.pro)

## TIME_DOUBLE

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    FUNCTION: time_double(time)
    NAME:
      time_double
    PURPOSE:
     A fast, vectorized routine that returns the number of seconds since 1970.
    INPUT:  input can be any of the following types:
      double(s)      seconds since 1970   (returns the input)
      string(s)      format:  YYYY-MM-DD/hh:mm:ss  see "time_string"
      structure(s)   format returned in "time_struct"
      long array     (MUST be 2 dimensional!)  PB5 time  (req. by CDF)

    OUTPUT:
      double, number of seconds since 1970  (UNIX time)
    KEYWORDS:
      EPOCH:  if set, it implies the input is double precision EPOCH time.

    SEE ALSO:  "time_string", "time_struct", "time_epoch", "time_pb5"

    NOTE:
      This routine works on vectors and is designed to be fast.
      Output will have the same dimensions as the input
      Out of range values are interpreted correctly.
      ie.  1994-13-1/12:61:00  will be treated as:  1995-1-1/13:01:00

    CREATED BY:    Davin Larson  Oct 1996
    FILE:  time_double.pro
    VERSION:  1.9
    LAST MODIFICATION:  01/07/12

(See ssl_general/misc/time_double.pro)

## TIME_EPOCH

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    NAME:
      time_epoch
    PURPOSE:
      Returns the EPOCH time required by CDF files.
    USAGE:
      epoch = time_epoch(t)
     NOT TESTED!!!

    CREATED BY:	Davin Larson  Oct 1996
    FILE:  time_epoch.pro
    VERSION:  1.1
    LAST MODIFICATION:  96/10/16

(See ssl_general/misc/time_epoch.pro)

## TIME_PB5

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    NAME:
      time_pb5
    PURPOSE:
      Returns the PB5 time required by CDF files.
    USAGE:
      pb5 = time_pb5(t)
    OUTPUT:
      2 dimensional long integer array with dimensions:  (n,3)  Where n is the number
      of elements in t
    Not fully TESTED!!!!

    CREATED BY:	Davin Larson  Oct 1996
    FILE:  time_pb5.pro
    VERSION:  1.3
    LAST MODIFICATION:  97/01/27

(See ssl_general/misc/time_pb5.pro)

## TIME_STAMP

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    PROCEDURE:   time_stamp,charsize=charsize
    PURPOSE:
         Prints a time stamp along the lower right edge of the current plot box
    KEYWORDS:
         CHARSIZE:  The character size to be used.  Default is !p.charsize/2.
         ON:        if set, then timestamping is turned on. (No other action taken)
         OFF:       if set, then timestamping is turned off. (Until turned ON)

(See ssl_general/misc/time_stamp.pro)

## TIME_STRING

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    FUNCTION: time_string(TIME)
    NAME:
      time_string
    PURPOSE:
      Converts time to a date string.
    INPUTs:
      TIME  input can be a scalar or array of any dimension of type:
      double(s)      seconds since 1970
      string(s)      format:  YYYY-MM-DD/hh:mm:ss
      structure(s)   format:  given in "time_struct"
      float(s)
      longs(s)
                     values outside normal range will be corrected.
    KEYWORDS:

      LOCAL_TIME ;      if set then local time is displayed.

      TFORMAT:   a format string such as:  "YYYY-MM-DD/hh:mm:ss.ff DOW TDIFF"
                   the following tokens are recognized:
                        YYYY  - 4 digit year
                        yy    - 2 digit year
                        MM    - 2 digit month
                        DD    - 2 digit date
                        hh    - 2 digit hour
                        mm    - 2 digit minute
                        ss    - 2 digit seconds
                        .fff   - fractional seconds
                        MTH   - 3 character month
                        DOW   - 3 character Day of week
                        DOY   - 3 character Day of Year
                        TDIFF - 5 character, hours different from UTC    (useful with LOCAL keyword)

            if TFORMAT is defined then the following keywords are ignored.

      FORMAT:         specifies output format.
        FORMAT=0:  YYYY-MM-DD/hh:mm:ss
        FORMAT=1:  YYYY Mon dd hhmm:ss
        FORMAT=2:  YYYYMMDD_hhmmss
        FORMAT=3:  YYYY MM dd hhmm:ss
        FORMAT=4:  YYYY-MM-DD/hh:mm:ss
        FORMAT=5:  YYYY/MM/DD hh:mm:ss
        FORMAT=6:  YYYYMMDDhhmmss
      SQL:            produces output format: "YYYY-MM-DD hh:mm:ss.sss"
                      (quotes included) which convenient for building SQL queries.
      PRECISION:      specifies precision
          -5:   Year only
          -4:   Year, month
          -3:   Year, month, date
          -2:   Year, month, date, hour
          -1:   Year, month, date, hour, minute
           0:   Year, month, date, hour, minute, sec
          >0:   fractional seconds
      AUTOPREC  If set PREC will automatically be set based on the array of times
      DELTAT:   (float) PREC set based on this precision.
      DATE_ONLY:   Same as PREC = -3
      MSEC:        Same as PREC = 3

    OUTPUT:
      string with the following format: YYYY-MM-DD/hh:mm:ss (Unless
      modified by keywords.)

    See Also:  "time_double"  , "time_struct" or "time_ticks"

    NOTE:
      This routine works on vectors and is designed to be fast.
      Output will have the same dimensions as the input.

    CREATED BY:    Davin Larson  Oct 1996
    FILE:  time_string.pro
    VERSION:  1.14
    LAST MODIFICATION:  02/11/01

(See ssl_general/misc/time_string.pro)

## TIME_STRUCT

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    FUNCTION: time_struct(time)
    NAME:
      time_struct
    PURPOSE:
     A fast, vectorized routine that returns a time structure.
    INPUT:  input can be any of the following types:
      double(s)      seconds since 1970
      string(s)      format:  YYYY-MM-DD/hh:mm:ss
      structure(s)   similar to format below.

    OUTPUT:
      structure with the following format:
    ** Structure TIME_STRUCT, 11 tags, length=40:
       YEAR            INT           1970            ; year    (0-14699)
       MONTH           INT              1            ; month   (1-12)
       DATE            INT              1            ; date    (1-31)
       HOUR            INT              0            ; hours   (0-23)
       MIN             INT              0            ; minutes (0-59)
       SEC             INT              0            ; seconds (0-59)
       FSEC            DOUBLE           0.0000000    ; fractional seconds (0-.999999)
       DAYNUM          LONG            719162        ; days since 0 AD  (subject to change)
       DOY             INT              0            ; day of year (1-366)
       DOW             INT              3            ; day of week  (subject to change)
       SOD             DOUBLE           0.0000000    ; seconds of day
       DST        =    INT      = 0                  ; Daylight saving time flag
       TZONE      =    INT      = 0                  ; Timezone  (Pacific time is -8)
       TDIFF      =    INT      = 0                  ; Hours from UTC

    See Also:  "time_double", "time_string", "time_epoch", "time_pb5"

    NOTE:
      This routine works on vectors and is designed to be fast.
      Output will have the same dimensions as the input

    CREATED BY:    Davin Larson  Oct 1996
    FILE:  time_struct.pro
    VERSION:  1.15
    LAST MODIFICATION:  02/11/01

(See ssl_general/misc/time_struct.pro)

## TIME_TICKS

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    FUNCTION:  time_tk_str = time_ticks(timerange,offset)
    NAME:
      time_ticks
    PURPOSE:
      Returns a structure that can be used to create time ticks for a plot.
      See "timetick" for more info
    INPUT:
      timerange: Two element vector specifying the time range of the plot
          this input can be obtained from: "time_double", "time_struct"
          or "time_string"
      offset: named variable in which offset time is placed.
    KEYWORDS:
      NUM_LAB_MIN:   minimum number of labels for bottom axis.

    OUTPUT:
      a structure that can be used with the _EXTRA keyword of the PLOT routine

    See Also: "box", "tplot"

     NOTES:

         The returned time_tk_str has tags named so that it can be used
         with the special _EXTRA keyword in the call to PLOT or OPLOT.

         The offset value that is returned from timetick must be
         subtracted from the time-axis data values before plotting.
         This is to maintain resolution in the PLOT routines, which use
         single precision floating point internally.  Remember that if
         the CURSOR routine is used to read a cursor position from the
         plot, this offset will need to be added back to the time-axis
         value to get seconds since  1970-01-01/00:00:00.

    NOTE:
      This routine is an enhanced version of the routine "timetick"
      See this routine for more info on usage

    WARNING!:
      This routine does not yet work on very small time scales.

    CREATED BY:	Davin Larson  Oct 1996
    FILE:  time_ticks.pro
    VERSION:  1.16
    LAST MODIFICATION:  02/04/17

(See ssl_general/misc/time_ticks.pro)

## TKM2RE

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    Procedure: tKm2Re

    Purpose: Converts a variable to RE or KM

    Inputs: name: a string naming the tplot variable to be modified
                  globbing may be used

    Keywords:
              newname: set this keyword to a string to store the
                       output in(only works when globbing is not used)
              suffix:  set this keyword to a string indicating the
                       suffix to be appended to the input variable(s)
              /replace: set this option to replace the variable being modified
              /KM : converts to KM from RE rather than to RE from KM

      examples:
            tKm2Re,'thb_state_pos'
            tKm2Re,'thb_state_pos',/replace
            tKm2Re,'thb_state_pos',/KM
            tKm2Re,'thb_state_pos',newname='pos_in_re'
            tKm2Re,'th?_state_pos',suffix='_converted'

      NOTES: Uses conversion of 6374.4 KM/RE
             By default output will be called: input_name+'_RE'

    $LastChangedBy: pcruce $
    $LastChangedDate: 2008-07-30 17:43:17 -0700 (Wed, 30 Jul 2008) $
    $LastChangedRevision: 3320 $
    $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/tkm2re.pro $

(See ssl_general/misc/tkm2re.pro)

## TPWRSPC[2]

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    NAME:
     tpwrspc
    PURPOSE:
     wrapper for pwrspc.pro allowing input of a tplot variable name.
        A Hanning window is applied to
        the input data, and its power is divided out of the returned
        spectrum. A straight line is subtracted from the data to
        reduce spurius power due to sawtooth behavior of a background.
        UNITS ARE (UNITS)^2 WHERE UNITS ARE THE UNITS OF quantity. freq
        is in 1/timeunits.
        THUS THE OUTPUT REPRESENTS THE MEAN SQUARED AMPLITUDE OF THE SIGNAL
           AT EACH SPECIFIC FREQUENCY. THE TOTAL (SUM) POWER UNDER THE CURVE IS
           EQUAL TO THE MEAN (OVER TIME) POWER OF THE OSCILLATION IN TIME DOMAIN.

    CALLING SEQUENCE:

    CALLING SEQUENCE:
     tpwrspc, varnames, newname=newname,_extra=_extra
    INPUT:
     varname = one tplot variable name
    KEYWORDS:
     newname = if set,give this name to the new data, the
               default is to append '_pwrspc' to the input name and
               pass out the name in the newname variable,
               Unless /overwrite is set
     overwrite = if set, write the new data back to the old tplot
                 variable, do not set this with newname
     noline = if set, no straight line is subtracted
     nohanning = if set, then no hanning window is applied to the input
     bin = a binsize for binning of the frequency data, the default is 3
     notperhz = if set, the output units are simply the square of the
                input units
     err_msg = named variable that contains any error message that might occur

     NOTES: 1. IF KEYWORD notperhz IS SET, THEN POWER IS IN UNITS^2. If notset
               power is (as normal) in UNITS^2/Hz.
            2. Inputs must be 1-dimensional.   For example, if you try to
                call this on a 3-d vector like fgs data, it will not work.
                call 'split_vec' first, to split the quantity into its components.

    HISTORY:
     27-mar-2007, jmm, jimm.ssl.berkeley.edu

    $LastChangedBy$
    $LastChangedDate$
    $LastChangedRevision$
    $URL$

(See ssl_general/misc/tpwrspc.pro)

## TRANGE_STR

[Previous Routine] [Next Routine] [List of Routines]

    FUNCTION:   trange_str,t1,t2
    INPUT:  t1,t2   doubles,   seconds since 1970
    OUTPUT:  string  with the format:  'YYYY-MM-DD/HH:MM:SS - HH:MM:SS'

    CREATED BY:	Davin Larson
    LAST MODIFICATION:	@(#)trange_str.pro	1.10 97/12/22

(See ssl_general/misc/trange_str.pro)

## TSMOOTH_IN_TIME

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    PROCEDURE: tsmooth_in_time, varname, dt, newname = newname
    PURPOSE:
     Calls smooth_in_time function on a plot variable
    INPUT:
     varname = variable passed to get_data, example - thg_mag_ccnv
     dt = the averaging time (in seconds)
    KEYWORDS:
     newname: set output variable name

    HISTORY:
     11-apr-2008, jmm, jimm@ssl.berkeley.edu

    $LastChangedBy: pcruce $
    $LastChangedDate: 2010-01-26 12:04:30 -0800 (Tue, 26 Jan 2010) $
    $LastChangedRevision: 7151 $
    $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/tsmooth_in_time.pro $

(See ssl_general/misc/tsmooth_in_time.pro)

## TSUB_AVERAGE

[Previous Routine] [Next Routine] [List of Routines]

    NAME:
     tsub_average
    PURPOSE:
     Subtracts average or median values from the data in a tplot
     variable, returns a new variable, only one at a time for now
    CALLING SEQUENCE:
     tsub_average, varname, out_name, new_name=new_name,median=median
    INPUT:
     varname =  a tplot variable name
    OUTPUT:
     out_name = variable name of the output tplot variable
    KEYWORDS:
     new_name = can be used to input the new variable name, if not input
     the default is to add a '-d' to the input name (or '-m' for median
     subtraction) and the name is passed out in this variable
    HISTORY:
     18-jul-2007, jmm, jimm@ssl.berkeley.edu
     02-nov-2007, jmm, Fixed bug for variables with no data.
     06-may-2008, jmm, Fixed problem, by changing non-float and
                       non-double datatypes to floats
    $LastChangedBy: $
    $LastChangedDate: $
    $LastChangedRevision: $
    $URL: $

(See ssl_general/misc/tsub_average.pro)

## TVECTOT

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    Procedure: tvectot(tplot vector total)

    Purpose: Add or remove the magnitude of a vector to a tplot quantity

    Inputs: name: a string naming the tplot variable to be modified,  may
    use regex

    Keywords: /remove: set this keyword to remove the magnitude from
                       vector
              newname: set this keyword to a string to store the(this
              option will not work properly if regex is used)
              output in a different variable instead of overwriting
              tot: set this keyword to a named variable to store
                 the magnitude as an array or set it to a string to store
                 the magnitude as a tplot variable(this option will not
                 work properly if regex is used)

      examples:
            tvectot,'tha_fgs_dsl'
            tvectot,'tha_fgs_dsl',/remove
            tvectot,'tha_fg*_dsl'
            tvectot,'tha_fgs_dsl',newname='tha_fgs_dsl_mag'
            tvectot,'tha_fgs_dsl',tot=var
            tvectot,'tha_fgs_dsl',tot='mag_t_var'

    $LastChangedBy: pcruce $
    $LastChangedDate: 2008-01-24 13:48:09 -0800 (Thu, 24 Jan 2008) $
    $LastChangedRevision: 2312 $
    $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/tvectot.pro $

(See ssl_general/misc/tvectot.pro)

## UNDEFINED

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    NAME:
     undefined
    PURPOSE:
     Tests whether a variable is undefined
    CALLING SEQUENCE:
     if ~undefined(var) then print,'Hooray!'

     INPUT:
      var:  A variable to be tested

    OUTPUT:
     1 on success, 0 on fail

     $LastChangedBy: pcruce $
     $LastChangedDate: 2008-07-28 11:53:49 -0700 (Mon, 28 Jul 2008) $
     $LastChangedRevision: 3311 $
     $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/undefined.pro $

(See ssl_general/misc/undefined.pro)

## WI

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    PROCEDURE:     wi, wnum

    PURPOSE:   Switch or open windows.

    INPUT:
       wnum - the window number.

    CREATED BY:    REE, 95-10-23
    completely rewritten by DEL 2006
    FILE: wi.pro
    VERSION: 1.6
    LAST MODIFICATION: 97/06/03

(See ssl_general/misc/wi.pro)

## XCLIP

[Previous Routine] [Next Routine] [List of Routines]

     xclip
    PURPOSE:
     Replaces with FLAGs the values of the array that are BEYOND
     the limits specified.
    CALLING SEQUENCE:
     xclip, amin, amax, y, flag=flag, _extra=_extra
    INPUT:
     amin, amax = the minumum and maximum values
     y = the input array
    OUTPUT:
     y = set to flag for points less than amin or greater than amax
    KEYWORDS:
     flag = the value that clipped data will be set to, the default is
               -0.0/0.0 (NaN)
     clip_adjacent = if set, then clip the vales adjacent to the bad
                     ones, as in tdespike_ae.pro
    HISTORY:
     2-feb-2007, jmm, jimm.ssl.berkeley.edu from Vassilis'
     clip_deflag.pro
     9-feb-2007, change big value to Nan
     9-oct-2007, added option to clip the points adjacent to the bad
                 ones, as in tdespike_ae.pro
     20-Oct-2007, Jmm, Added this comment to test commit comand
    $LastChangedBy$
    $LastChangedDate$
    $LastChangedRevision$
    $URL$

(See ssl_general/misc/xclip.pro)

## XDEFLAG

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     xdeflag
    PURPOSE:
     Replaces FLAGs in arrays with interpolated or other values
    CALLING SEQUENCE:
     xdeflag, method, t, y, flag=flag, _extra=_extra
    INPUT:
     method = set to "repeat", this will repeat the last good value.
              set to "linear", then linear interpolation is used, but for
              the edges, the closest value is used, there is no
              extrapolation
     t = time array, in any useable tplot format
     y = the input array, n_elements(t) by n
    OUTPUT:
     y = either interpolated or repated, where the value is > 0.98*flag,
         or NaN
    KEYWORDS:
     flag = all values greater than 0.98 times this value will be removed;
            default is 6.879e28, NaNs and +/-Infinity are always removed
     maxgap = the maximum number of rows that can be filled? the default
               is n_elements(t)
    HISTORY:
     2-feb-2007, jmm, jimm.ssl.berkeley.edu from Vassilis' clip_deflag.pro

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(See ssl_general/misc/xdeflag.pro)

## XDEGAP

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    NAME:
     xdegap
    PURPOSE:
     Locates gaps in data, and fills in with NaN
     This subroutine accepts the time array (can be cline time) t and the
     multi-dimensional array yarr that matches with the time array.
     It outputs the same arrays but with a different number of rows
     depending on how many rows were added. It then figures out where to
     add rows by checking which time differences are greater than or equal to
     deltat plus a margin and adds an array of rows of equispaced times of
     size tstep=gap/(number_of_points_that_fit_with_minimum_cumulative_error).
     The same number of rows is added to yarr with values equal to
     FLAGs.
     NOTE: ARRAYS AND STRUCTURES THAT NEED DEGAPPING ARE REDEFINED TO BE
     LARGER THAN BEFORE. THUS THE TIME COLUMN THAT HAS BEEN DEGAPPED
     WILL NOT CORRESPOND TO THE ELEMENTS OF AN ARRAY THAT HAS NOT BEEN
     DEGAPPED. CAUTION: DEGAP ALL ARRAYS OR STRUCTURES YOU ARE GOING TO USE
     TOGETHER, I.E., WITH ONE DEGAP CALL.
     ADDITIONAL NOTE: To conserve memory, see the ONENANPERGAP keyword.
    CALLING SEQUENCE:
     xdegap, dt, margin, ct, y, ct_out, y_out [,/nowarning] [,maxgap = <value>] [,iindices=<variable>] [,/onenanpergap]
    INPUT:
     dt = the time interval for tests
     margin = the margin
     ct = the input time array
     y = the input array, can be 1 or 2d (n_elements(ct), m)
    OUTPUT:
     ct_out = the output time array,
     y_out = the input time array
    KEYWORDS:
     nowarning = if set, suppresses warnings
     maxgap = the maximum gap size filled, in seconds
     iindicies = the indices in the output arrays that contain the original data
     flag = A numeric user-specified value to use for flagging gaps.
       Defaults to a floating NaN.  If an array is entered, only the
       first element is considered.If a non-numeric datatype is entered,
       its value is ignored.
     onenanpergap = Fill gaps with only one NaN -> useful for conserving memory.
       Also, for reference concerning post-processing, the INTERPOL function
       propagates a single NaN just as it would many NaNs.
     gap_begin = the double-precision start times of the detected gaps.
     gap_end = the double-precision end times of the detected gaps.
    HISTORY:
     From Vassilis' degap.pro, 2-apr-2007, jmm, jimm@ssl.berkeley.edu
     bug fix for undefined variable, jmm, 24-jun-2007
     Switched maxgap to seconds, jmm, 26-oct-2007
     Added comment to test svn version 4_00, jmm, 28-apr-2008
     Added ONENANPERGAP kw, W.M.F., 5 May, 2009.
     Added GAP_BEGIN, GAP_END kwd's, 12 June, 2009.
    Added _extra keyword, 20-oct-2009, jmm
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(See ssl_general/misc/xdegap.pro)

## [4]

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    NAME:

      fancompress

    PURPOSE:
      Decimates polylines in an aesthetically pleasing fashion.

    CALLING SEQUENCE:
      outidx = fancompress(inpts,err)

    INPUT:
      inpts: N x 2 dimension array, where inpts[*,0] are the x components of the polyline and inpts[*,1] are the y components of the polyline
      err: The amount of error allowed before including a point

    Keywords:
      vector:  Will enable the vectorized fan compression algorithm.
      step:  Controls the number of steps to perform per loop, during vectorized implementation.
             At the limit, where step = N, the vectorized version works like the iterative
             version.
    OUTPUT:
      An array of indexes into inpts.  Indices will range from 0 to N-1.  First and Last points are always included.

    NOTES:
      1. Based almost entirely on the paper:
      Fowell, Richard A. and McNeil, David D. , “Faster Plots by Fan Data-Compression,”
      IEEE Computer Graphics & Applications, Vol. 9, No. 2,Mar. 1989, pp. 58-66.

      2. One modification from published algorithm, handles NaNs by always including the point
      before a group of NaNs, 1 NaN and the point after the NaNs.  This ensures that gaps will
      be drawn accurately.

      3. Algorithm is fairly slow, because it requires 1 pass over all data points.
      Optimizing this algorithm by divide and conquer, vectorization, or dlm may be
      a worthwhile use of time in the future.

      4. Vectorized version is essentially a divide and conquer version of the Fowell & McNeil algorithm.
      The idea being to split the array into sub-problems that can be addressed in parallel using IDL vector-ops.
      The fan-comparison operation at the core of the fan-compression algorithm takes 3-sequential points to work.
      So if step = 1, the algorithm will split the input array of length N in floor(N/3) segments; Making an independent
      decision on whether to keep the middle point of each segment, based upon the start and end points of each segment.
      If a point is removed, the 5-element fan vector at the start point is updated, and this will be applied in the subsequent test.

      5. If step is higher an internal loop will perform the operation iteratively within-segments, but in parallel across segments.
      For example, If step is 3, N will be split into floor(N/5) segments(5-point segments). Operating on points 1-2-3 of the segment
      in the first iteration of the internal loop, points 1-3-4 or 2-3-4 on the second iteration and points 1-4-5,2-4-5,or 3-4-5 on the
      third iteration. Which sequence ends up being operated on depends on whether the point was accepted or rejected in the previous iteration.

      6. Vectorized(step=1) version generally achieves a speed up of 1000% at decrease in compression by ~10%.
         For example, if the iterative version creates a 1 Mb of output in 1 sec, this will create
         1.1 Mb of output in .1 sec.  Higher values of step, tend to decrease compression rates until step becomes large,
         then compression approaches the iterative solution

    $LastChangedBy: pcruce $
    $LastChangedDate: 2009-07-27 17:44:33 -0700 (Mon, 27 Jul 2009) $
    $LastChangedRevision: 6496 $
    $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/misc/fancompress.pro $

(See ssl_general/misc/fancompress.pro)