Identifier     chk_multix

 Purpose        check if an array of x values (xscale) contains multiple
                points at the same value. If so, compute mean of the 
                corresponding y values (yarr) and sigma values (sarr)
                at the mean of the duplicate points in xarr and modify 
                xarr, yarr and sarr accordingly.
                This is intended as a pre-binning operation to simplify
                interpolation and rebinning of a spectrum.


 Synopsis       status = chk_multix(xarr, yarr, sarr , epsilon, /mean)


 Arguments      Name      I/O Type       Description
                -----------------------------------------------------
                xarr      I/O  Fltarr     x-scale (e.g. wavelength array that
                                          is to be resampled)
                yarr      I/O  Fltarr     y-scale (e.g. flux array that
                                          is to be resampled)
                sarr      I/O  Fltarr     sigma array for yarr
                epsilon   I    Float      acceptable minimum seperation between
                                          wavelength (micron) points in the output
                                          array.
                mean      I     --        If this option is set, arithmatic
                                          mean values are computed instead
                                          of weighted mean. This option must
                                          be used if the sigma array has any zero
                                          values.


 Returns        Modifies xarr, yarr, sarr, and status (1 for fatal, 0 otherwise)


 Description    - Check if xscale contains multiple points
                  at the "same" value ("same" means value +- epsilon). If so,
                  compute mean of these multiple x values and the mean values
                  of the corresponding yarr and sarr points. Replace the
                  multiple points in xarr, yarr and sarr with their mean
                  values (weighted by (1./sigma)^2 or not depending on /mean
                  option). 

 Comment


 Example        stat = chk_multix(wave, flux, stdev, .0001)

 Dependencies   CALLS: kwd_notset, sap_error
                CALLED FROM: glue, sap_rebin

 Category       ISAP

 Filename       chk_multix.pro

 Author         Iffat R. Khan (irk@ipac.caltech.edu)

 Version        0.3

 History        0.1 27.07.95  definition of requirements - first draft   E. Sturm 
                0.1 01.09.95  revision of requirements   -  J. Mazz (mazz@ipac.caltech.edu)
                0.1 01.09.95  Version 0.1   --> irk@ipac
                0.2 01-11-95  Revised parameters    --> irk@ipac
                              checking/Error messages
                1.0 24-05-96  changed usage to FUNCTION from PRO    --> irk@ipac
                              to incorporate error status flag

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Copyright (C) 1995, California Institute of Technology.  ;
U.S. Government Sponsorship under NASA Contract NAS7-918 ;
is acknowledged.                                         ;
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