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<title>GNU Scientific Library – Reference Manual: Example programs for 2D histograms</title>
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<a name="Example-programs-for-2D-histograms"></a>
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<p>
Previous: <a href="Resampling-from-2D-histograms.html#Resampling-from-2D-histograms" accesskey="p" rel="previous">Resampling from 2D histograms</a>, Up: <a href="Histograms.html#Histograms" accesskey="u" rel="up">Histograms</a> [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Example-programs-for-2D-histograms-1"></a>
<h3 class="section">22.22 Example programs for 2D histograms</h3>
<p>This program demonstrates two features of two-dimensional histograms.
First a 10-by-10 two-dimensional histogram is created with x and y running
from 0 to 1. Then a few sample points are added to the histogram, at
(0.3,0.3) with a height of 1, at (0.8,0.1) with a height of 5 and at
(0.7,0.9) with a height of 0.5. This histogram with three events is
used to generate a random sample of 1000 simulated events, which are
printed out.
</p>
<div class="example">
<pre class="verbatim">#include <stdio.h>
#include <gsl/gsl_rng.h>
#include <gsl/gsl_histogram2d.h>
int
main (void)
{
const gsl_rng_type * T;
gsl_rng * r;
gsl_histogram2d * h = gsl_histogram2d_alloc (10, 10);
gsl_histogram2d_set_ranges_uniform (h,
0.0, 1.0,
0.0, 1.0);
gsl_histogram2d_accumulate (h, 0.3, 0.3, 1);
gsl_histogram2d_accumulate (h, 0.8, 0.1, 5);
gsl_histogram2d_accumulate (h, 0.7, 0.9, 0.5);
gsl_rng_env_setup ();
T = gsl_rng_default;
r = gsl_rng_alloc (T);
{
int i;
gsl_histogram2d_pdf * p
= gsl_histogram2d_pdf_alloc (h->nx, h->ny);
gsl_histogram2d_pdf_init (p, h);
for (i = 0; i < 1000; i++) {
double x, y;
double u = gsl_rng_uniform (r);
double v = gsl_rng_uniform (r);
gsl_histogram2d_pdf_sample (p, u, v, &x, &y);
printf ("%g %g\n", x, y);
}
gsl_histogram2d_pdf_free (p);
}
gsl_histogram2d_free (h);
gsl_rng_free (r);
return 0;
}
</pre></div>
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