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<title>The GNU Fortran Compiler: RANDOM_NUMBER</title>
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<a name="RANDOM_005fNUMBER"></a>
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<p>
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Next: <a href="RANDOM_005fSEED.html#RANDOM_005fSEED" accesskey="n" rel="next">RANDOM_SEED</a>, Previous: <a href="RAND.html#RAND" accesskey="p" rel="prev">RAND</a>, Up: <a href="Intrinsic-Procedures.html#Intrinsic-Procedures" accesskey="u" rel="up">Intrinsic Procedures</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
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<a name="RANDOM_005fNUMBER-_002d_002d_002d-Pseudo_002drandom-number"></a>
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<h3 class="section">9.215 <code>RANDOM_NUMBER</code> — Pseudo-random number</h3>
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<a name="index-RANDOM_005fNUMBER"></a>
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<a name="index-random-number-generation-3"></a>
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<dl compact="compact">
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<dt><em>Description</em>:</dt>
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<dd><p>Returns a single pseudorandom number or an array of pseudorandom numbers
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from the uniform distribution over the range <em>0 \leq x < 1</em>.
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</p>
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<p>The runtime-library implements George Marsaglia’s KISS (Keep It Simple
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Stupid) random number generator (RNG). This RNG combines:
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</p><ol>
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<li> The congruential generator <em>x(n) = 69069 \cdot x(n-1) + 1327217885</em>
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with a period of <em>2^{32}</em>,
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</li><li> A 3-shift shift-register generator with a period of <em>2^{32} - 1</em>,
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</li><li> Two 16-bit multiply-with-carry generators with a period of
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<em>597273182964842497 > 2^{59}</em>.
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</li></ol>
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<p>The overall period exceeds <em>2^{123}</em>.
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</p>
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<p>Please note, this RNG is thread safe if used within OpenMP directives,
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i.e., its state will be consistent while called from multiple threads.
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However, the KISS generator does not create random numbers in parallel
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from multiple sources, but in sequence from a single source. If an
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OpenMP-enabled application heavily relies on random numbers, one should
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consider employing a dedicated parallel random number generator instead.
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</p>
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</dd>
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<dt><em>Standard</em>:</dt>
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<dd><p>Fortran 95 and later
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</p>
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</dd>
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<dt><em>Class</em>:</dt>
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<dd><p>Subroutine
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</p>
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</dd>
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<dt><em>Syntax</em>:</dt>
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<dd><p><code>RANDOM_NUMBER(HARVEST)</code>
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</p>
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</dd>
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<dt><em>Arguments</em>:</dt>
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<dd><table>
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<tr><td width="15%"><var>HARVEST</var></td><td width="70%">Shall be a scalar or an array of type <code>REAL</code>.</td></tr>
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</table>
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</dd>
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<dt><em>Example</em>:</dt>
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<dd><div class="smallexample">
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<pre class="smallexample">program test_random_number
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REAL :: r(5,5)
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CALL init_random_seed() ! see example of RANDOM_SEED
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CALL RANDOM_NUMBER(r)
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end program
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</pre></div>
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</dd>
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<dt><em>See also</em>:</dt>
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<dd><p><a href="RANDOM_005fSEED.html#RANDOM_005fSEED">RANDOM_SEED</a>
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</p></dd>
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</dl>
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