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<title>Random Number Generator Examples - GNU Scientific Library -- Reference Manual</title>
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Next: <a rel="next" accesskey="n" href="Random-Number-References-and-Further-Reading.html">Random Number References and Further Reading</a>,
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<h3 class="section">17.13 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),
<pre 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></pre>
<p class="noindent">Here is the output of the program,
<pre class="example"> $ ./a.out
<pre class="verbatim"> 0.99974
0.16291
0.28262
0.94720
0.23166
0.48497
0.95748
0.74431
0.54004
0.73995
</pre></pre>
<p class="noindent">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>,
<pre class="example"> $ GSL_RNG_SEED=123 GSL_RNG_TYPE=mrg ./a.out
<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></pre>
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