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<title>GNU Scientific Library – Reference Manual: Random Number Generator Examples</title>
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<a name="Random-Number-Generator-Examples"></a>
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<p>
Next: <a href="Random-Number-References-and-Further-Reading.html#Random-Number-References-and-Further-Reading" accesskey="n" rel="next">Random Number References and Further Reading</a>, Previous: <a href="Random-Number-Generator-Performance.html#Random-Number-Generator-Performance" accesskey="p" rel="previous">Random Number Generator Performance</a>, Up: <a href="Random-Number-Generation.html#Random-Number-Generation" accesskey="u" rel="up">Random Number Generation</a> [<a href="Function-Index.html#Function-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Examples-11"></a>
<h3 class="section">18.13 Examples</h3>
<p>The following program demonstrates the use of a random number generator
to produce uniform random numbers in the range [0.0, 1.0),
</p>
<div class="example">
<pre class="verbatim">#include <stdio.h>
#include <gsl/gsl_rng.h>
int
main (void)
{
const gsl_rng_type * T;
gsl_rng * r;
int i, n = 10;
gsl_rng_env_setup();
T = gsl_rng_default;
r = gsl_rng_alloc (T);
for (i = 0; i < n; i++)
{
double u = gsl_rng_uniform (r);
printf ("%.5f\n", u);
}
gsl_rng_free (r);
return 0;
}
</pre></div>
<p>Here is the output of the program,
</p>
<div class="example">
<pre class="example">$ ./a.out
</pre><pre class="verbatim">0.99974
0.16291
0.28262
0.94720
0.23166
0.48497
0.95748
0.74431
0.54004
0.73995
</pre></div>
<p>The numbers depend on the seed used by the generator. The default seed
can be changed with the <code>GSL_RNG_SEED</code> environment variable to
produce a different stream of numbers. The generator itself can be
changed using the environment variable <code>GSL_RNG_TYPE</code>. Here is the
output of the program using a seed value of 123 and the
multiple-recursive generator <code>mrg</code>,
</p>
<div class="example">
<pre class="example">$ GSL_RNG_SEED=123 GSL_RNG_TYPE=mrg ./a.out
</pre><pre class="verbatim">GSL_RNG_TYPE=mrg
GSL_RNG_SEED=123
0.33050
0.86631
0.32982
0.67620
0.53391
0.06457
0.16847
0.70229
0.04371
0.86374
</pre></div>
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