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<title>GNU Scientific Library &ndash; 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> &nbsp; [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Example-programs-for-2D-histograms-1"></a>
<h3 class="section">23.22 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 &lt;stdio.h&gt;
#include &lt;gsl/gsl_rng.h&gt;
#include &lt;gsl/gsl_histogram2d.h&gt;

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-&gt;nx, h-&gt;ny);
    
    gsl_histogram2d_pdf_init (p, h);

    for (i = 0; i &lt; 1000; i++) {
      double x, y;
      double u = gsl_rng_uniform (r);
      double v = gsl_rng_uniform (r);
       
      gsl_histogram2d_pdf_sample (p, u, v, &amp;x, &amp;y);
      
      printf (&quot;%g %g\n&quot;, x, y);
    }

    gsl_histogram2d_pdf_free (p);
  }

  gsl_histogram2d_free (h);
  gsl_rng_free (r);

  return 0;
}
</pre></div>






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