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    Plot data points with accompanying X or Y error bars.


    This is a greatly enhanced version of the standard IDL Library routine

Calling Sequence

    ploterror, [ x,] y, [xerr], yerr [, TYPE=, /NOHAT, HATLENGTH= , NSUM =
                  ERRTHICK=, ERRSTYLE=, ErrcolOR=, NSKIP=, .. PLOT keywords]


    X = array of abcissae.
    Y = array of Y values.
    XERR = array of error bar values (along X)
    YERR = array of error bar values (along Y)

Optional Input Keyword Parameters

    TYPE = type of plot produced. The possible types are:
              TYPE = 0 : X Linear - Y Linear (default)
              TYPE = 1 : X Linear - Y Log
              TYPE = 2 : X Log - Y Linear
              TYPE = 3 : X Log - Y Log
              Actually, if 0 is specified, the XLOG and YLOG keywords
              are used. If these aren't specified, then a linear-linear
              plot is produced. This keyword is available to maintain
              compatibility with the previous version of PLOTERROR.
    /NOHAT = if specified and non-zero, the error bars are drawn
              without hats.
    HATLENGTH = the length of the hat lines in device units used to cap the
              error bars. Defaults to !D.X_VSIZE / 100).
    ERRTHICK = the thickness of the error bar lines. Defaults to the
              THICK plotting keyword.
    ERRSTYLE = the line style to use when drawing the error bars. Uses
              the same codes as LINESTYLE.
    ERRCOLOR = String (e.g. 'red') or scalar integer (0 - !D.N_TABLE)
              specifying the color to use for the error bars. See CGCOLOR()
              for a list of possible color names. See
              for a warning about the use of indexed color
    NSKIP = Integer specifying the error bars to be plotted. For example,
              if NSKIP = 2 then every other error bar is plotted; if NSKIP=3
              then every third error bar is plotted. Default is to plot
              every error bar (NSKIP = 1)
    NSUM = Number of points to average over before plotting, default=!P.NSUM
            The errors are also averaged, and then divided by sqrt(NSUM).
            This approximation is meaningful only when the neighboring error
            bars have similar sizes. PLOTERROR does not pass the NSUM
            keyword to the PLOT command, but rather computes the binning
            itself using the FREBIN function.
    TRADITIONAL - If set to 0 then a black plot is drawn on a white background
            in the graphcis window. The default value is 1, giving the
            traditional black background for a graphics window.
    WINDOW - Set this keyword to plot to a resizeable graphics window
    Any valid keywords to the cgPLOT command (e.g. PSYM, YRANGE, AXISCOLOR
    SYMCOLOR, ASPECT) are also accepted by PLOTERROR via the _EXTRA facility.


      Arrays must not be of type string, and there must be at least 1 point.
      If only three parameters are input, they will be taken as X, Y and
      YERR respectively.
      PLOTERROR cannot be used for asymmetric error bars. Instead use
      OPLOTERROR with the /LOBAR and /HIBAR keywords.
      Any data points with NAN values in the X, Y, or error vectors are


      Suppose one has X and Y vectors with associated errors XERR and YERR
      (1) Plot Y vs. X with both X and Y errors and no lines connecting
          the points
                  IDL> ploterror, x, y, xerr, yerr, psym=3
      (2) Like (1) but plot only the Y errors bars and omits "hats"
                  IDL> ploterror, x, y, yerr, psym=3, /NOHAT
      This an enhanced version of the procedure PLOTERR in the standard IDL
      distribution. It was renamed from PLOTERR to PLOTERROR in June 1998
      in the IDL Astronomy Library to avoid conflict with the RSI procedure.


      A plot of X versus Y with error bars drawn from Y - YERR to Y + YERR
      and optionally from X - XERR to X + XERR is written to the output device

Procedure Calls

    cgPlot, cgPlots
    FREBIN - used to compute binning if NSUM keyword is present

Modification History

    William Thompson Applied Research Corporation July, 1986
    DMS, April, 1989 Modified for Unix
    Michael R. Greason ST Systems
    May, 1991 Added most of the plotting keywords, put hats
                              on the error bars.
    K. Venkatakrishna Added option to plot xerr, May, 1992
    Michael R. Greason Corrected handling of reversed axes. Aug. 1992
    W. Landsman Use _EXTRA keyword July 1995
    W. Landsman Plot more than 32767 points Feb 1996
    W. Landsman Fix Y scaling when only XRANGE supplied Nov 1996
    W. Landsman Added NSKIP keyword Dec 1996
    W. Landsman Use XLOG, YLOG instead of XTYPE, YTYPE Jan 1998
    W. Landsman Rename to PLOTERROR, OPLOTERROR Jun 1998
    W. Landsman Better default scaling when NSKIP supplied Oct 1998
    W. Landsman Ignore !P.PSYM when drawing error bars Jan 1999
    W. Landsman Handle NSUM keyword correctly Aug 1999
    W. Landsman Fix case of /XLOG but no X error bars Oct 1999
    W. Landsman Work in the presence of NAN values Nov 2000
    W. Landsman Improve logic when NSUM or !P.NSUM is set Jan 2001
    W. Landsman Only draw error bars with in XRANGE (for speed) Jan 2002
    W. Landsman Fix Jan 2002 update to work with log plots Jun 2002
    W. Landsman Added _STRICT_EXTRA Jul 2005
    W. Landsman/D.Nidever Fixed case of logarithmic axes reversed Mar 2009
    W. Landsman/S. Koch Allow input to be a single point Jan 2010
    W. Landsman Add Coyote Graphics Feb 2011
    W. Landsman Make keyword name ERRCOLOR instead of ECOLOR
                Speedup when no ERRCOLOR defined Feb 2011
    D. Fanning Use PLOTS instead of CGPLOTS for speed Jan 2012

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