NAME

       Histogram - This utility is used to generate histograms.  Histograms or bar charts are
       used to show the distribution of values in a like-sample dataset.  The individual values
       are sorted by size into a number of value ranges called class intervals.  The number of
       samples out of the total which fall into a class interval are represented as a histogram
       bar height.  The height of each histogram bar is proportional to the number of samples in
       that class interval.

       Various options are available including the specification of class values, spacing between
       histogram bars, shading of bars, windowing (i.e. scaling), specification of color, labels,
       titles, etc.  One can also detect and ignore missing data which has been assigned a
       special value.  Options are set by calls to routines HSTOPL, HSTOPR, HSTOPC, and HSTOPI.
       A call to routine HISTGR then generates the histogram.

SYNOPSIS

       HISTGR - Generates histograms with many options available via input arguments and internal
       parameter selections.

       HSTOPC - Sets values of internal parameters of type character.

       HSTOPI - Sets values of internal parameters of type integer.

       HSTOPL - Sets values of internal parameters of type logical.  Specifically, HSTOPL is used
       to turn options "OFF", or "ON".

       HSTOPR - Sets values of internal parameters of type real.

C-BINDING SYNOPSIS

       c_histgr
       c_hstopc
       c_hstopi
       c_hstopl
       c_hstopr

ACCESS

       To use the Histogram C or Fortran routines, load the NCAR Graphics libraries ncarg,
       ncarg_gks, and ncarg_c, preferably in that order.

MESSAGES

       The possible error messages are as follows:

       HISTGR - NPTS LESS THAN 1
              The argument NPTS, number of binable values, has been entered in error.

       HISTGR - NCLASS LESS THAN 1
              NCLASS, the number of histogram bars, has been entered in error.

       HISTGR - NPTS .GT. NDIM
              The argument NPTS, number of binable values, is larger than the array dimension
              size.  Reduce NPTS or modify the code to increase the array dimension size.  Set
              NDIM in the code to the new array dimension size.

       HISTGR - NWRK .LT. NDIM+3*NCLASS+3
              The argument NWRK, the dimension size of the work array, is incorrect.  Recompute
              it according to the above formula.

       HISTGR - NCLASS .NE. NPTS (IFLAG=2)
              IFLAG = 2 signals a special case in which the input data has already been
              accumulated into class intervals.  Therefore, the number of data values, NPTS, and
              the number of histogram bars, NCLASS, must be equal.

       HISTGR - NCLASS .NE. NPTS (IFLAG=3)
              IFLAG = 3 signals a special case in which the input data has already been
              accumulated into class intervals.  Therefore, the number of data values, NPTS, and
              the number of histogram bars, NCLASS, must be equal.  (IFLAG = 3 differs from the
              IFLAG = 2 case only in the fact that two histograms are to be displayed instead of
              one.)

       HISTGR - NCLASS MUST EQUAL NPTS
              This is a redundant test on whether the number of input data values, NPTS, equals
              the number of bars, NCLASS, when the IFLAG option is 2 or 3.

       HISTGR - IFLAG NOT SPECIFIED OR INVALID
              HISTGR argument IFLAG is not one of the legal values of 0, 1, 2, or 3.

       HISTGR - MIN. X-VALUE .EQ. MAX. X-VALUE
              A histogram has no width.  This probably means the values of HISTGR argument CLASS
              have been entered in error.

       HISTGR - MAXIMUM Y-VALUE .EQ. 0.0
              A histogram has no data.  The histogram is plotted with a Y range of .02.  This
              probably means the HISTGR argument DAT1 had all zero values.

       HISTGR - WINDOW OPTION ERROR, RANGE IS 0. - 1.
              The internal parameter options that define the part of the frame where the
              histogram is to be drawn have been entered incorrectly.

       HSTOPC - UNDEFINED OPTION

       HSTOPI - UNDEFINED OPTION

       HSTOPL - UNDEFINED OPTION

       HSTOPR - UNDEFINED OPTION
              Either an internal parameter name or value is incorrect.  Check the spelling in the
              calls to whichever routine is cited.

       HSTOPI - LCOL MUST EQUAL 8
              The number of color indices input to HSTOPI cannot exceed 8.

       HSTOPR - INVALID SPACING PARAMETER
              Either the spacing of histogram bars, or the overlap of bars from two histograms,
              is outside of the legal range.  Valid values for spacing of bars are 0.0 (no
              spacing) to 4.0 (maximum spacing.)  Valid values used to set overlap of adjacent
              histogram bars when comparing two datasets in one histogram are -4.0 (maximum
              overlap) to 4.0 (little or no overlap.)

SEE ALSO

       Online: histgr, histogram_params, hstopc, hstopi, hstopl, hstopr, ncarg_cbind

       Hardcopy: NCAR Graphics Fundamentals, UNIX Version

COPYRIGHT

       Copyright (C) 1987-2009
       University Corporation for Atmospheric Research
       The use of this Software is governed by a License Agreement.