HISTGR(3NCARG)

NAME
HISTGR - Plots a histogram with various options including specification of class values, spacing between histogram bars, shading of bars, windowing (i.e. scaling), specification of color, labels, titles, etc. Data values are partitioned into classes; histogram bars represent either number of occurrences within each class, or a Y-value associated with that class (user choice). Options are set by calls to subroutines HSTOPL, HSTOPR, HSTOPC, and HSTOPI before the call to HISTGR.

UTILITY
This routine is part of the Histogram utility in NCAR Graphics. To see the overview man page for this utility, type "man histogram".

SYNOPSIS
CALL HISTGR (DAT1,NDIM,NPTS,IFLAG,CLASS,NCLASS,WRK,NWRK)

C-BINDING SYNOPSIS
#include <ncarg/ncargC.h>

void c_histgr (float *dat1, int ndim, int npts,
int iflag, float *class, int nclass, float *wrk, int nwrk)

DESCRIPTION

DAT1
    Two dimensional real array containing data of one of two types, either values to be collected into class intervals before plotting, or values which have already been assigned to class intervals and only need to be displayed. See argument IFLAG for a more complete description of HISTGR input data options. DAT1 is dimensioned: DAT1(NDIM,2).

NDIM
    The size of the first dimension of DAT1 as set in the dimension statement of the calling program.

NPTS
    Number of values actually stored into DAT1 on this call. NPTS must always be less than or equal to NDIM.

IFLAG
    An integer flag which selects one of four options provided by the HISTGR utility. The options are:

    0 A single array of length NPTS is loaded
         into the DAT1 array. HISTGR computes NCLASS
         equally sized class intervals that vary
         from the minimum value in DAT1 to the
         maximum value in steps of (MAX-MIN)/NCLASS.

         All values of DAT1 that fall in each
         class interval are separately accumulated
         for that interval. The final tabulations
         are plotted as a histogram of NCLASS bars.
         The bar height can be labeled with the
         number of points that fall within this
         particular class interval (bin size), or
         it can be given as a percentage of the
         number of values input, NPTS.

         Note that under this option the user
         has no control over the range of the
         class intervals. They are internally
         determined from the range of the data.

    1 This option is similar to the IFLAG = 0
         option except that the user can select
         the range of the class intervals into
         which the data are collected. For example,
         say the user wants to collect the number
         of occurrences of the DAT1 values that
         fall within 5 equally spaced intervals
         in the value range from 0. to 10. The
         user would then input NCLASS+1 class
         interval end points into array CLASS,
         namely 0., 2., 4., 6., 8., and 10.
         These values need not be entered in
         monotonically increasing order and
         need not be equally spaced.

    2 This option allows the user to enter
         and display data which has already
         been accumulated into class intervals,
         i.e., already available histograms.
         The data input to DAT1 thus have
         percentage of total, or number of
         occurrences values. In this case the
         number of points in DAT1, NPTS, is
         equal to the number of class intervals
         (histogram bars), NCLASS. The NCLASS
         class interval midpoints are loaded
         into array CLASS. They do not have
         to be of equal width.

    3 This option is the same as option
         IFLAG = 2 except that two histograms
         can be displayed for comparison
         purposes. The first histogram is
         loaded into DAT1(NPTS,1). The second
         histogram is loaded into DAT1(NPTS,2).
         The first histogram can partially
         shade or obscure the second histogram
         by the appropriate selection of the
         SPAC and OVERLP options. Note that
         NPTS = NCLASS when IFLAG = 2 or 3.

CLASS
    Real array containing class values, dimensioned (NCLASS+1). This array has the following IFLAG dependencies:

    IFLAG = 0 CLASS is not used.

    IFLAG = 1 NCLASS+1 class interval end points
            are loaded into array CLASS in a
            monotonically increasing order. The
            intervals need not be of equal width.

    IFLAG = 2 NCLASS midpoint intervals are loaded
            into array CLASS. They must be in
            monotonically increasing order, but
            need not be of equal widths. The
            histogram bars will however be
            displayed with equal widths.

    IFLAG = 3 Same as for IFLAG = 2.

NCLASS
    Number of class intervals (histogram bars) specified. NCLASS must be .GE. 1.

WRK Real scratch array, dimensioned by NWRK in the dimension statement of the calling program.

NWRK
    The dimension size of array WRK determined from: NDIM + 3 * (NCLASS + 1)

C-BINDING DESCRIPTION
The C-binding argument descriptions are the same as the FORTRAN argument descriptions with the following exceptions:

dat1
    Two dimensional real array dimensioned: dat1(2,ndim).

ndim
    The size of the second dimension of dat1 as set in the dimension statement of the calling program.

USAGE
Many parameters which affect the output histogram can be set before this routine is called. See the histogram_params man page for a short functional description of all available parameters. For more detail on a specific option, see the man pages of the parameter setting routines (HSTOPC, HSTOPI, HSTOPL, or HSTOPR) used to set the parameters defining that option.

EXAMPLES
Use the command "ncargex thstgr" to generate a three frame example of various types of histograms. "ncargex thstmv" will show three examples of histograms with missing values in the input data.

ACCESS
To use HISTGR or c_histgr, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in that order.

MESSAGES
See the histogram man page for a description of all Histogram error messages and/or informational messages.

SEE ALSO
Online: histogram, 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.