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<h3 class="section">8.198 <code>RANDOM_SEED</code> — Initialize a pseudo-random number sequence</h3>
<p><a name="index-RANDOM_005fSEED-935"></a><a name="index-random-number-generation_002c-seeding-936"></a><a name="index-seeding-a-random-number-generator-937"></a>
<dl>
<dt><em>Description</em>:<dd>Restarts or queries the state of the pseudorandom number generator used by
<code>RANDOM_NUMBER</code>.
<p>If <code>RANDOM_SEED</code> is called without arguments, it is initialized to
a default state. The example below shows how to initialize the random
seed based on the system's time.
<br><dt><em>Standard</em>:<dd>Fortran 95 and later
<br><dt><em>Class</em>:<dd>Subroutine
<br><dt><em>Syntax</em>:<dd><code>CALL RANDOM_SEED([SIZE, PUT, GET])</code>
<br><dt><em>Arguments</em>:<dd>
<p><table summary=""><tr align="left"><td valign="top" width="15%"><var>SIZE</var> </td><td valign="top" width="70%">(Optional) Shall be a scalar and of type default
<code>INTEGER</code>, with <code>INTENT(OUT)</code>. It specifies the minimum size
of the arrays used with the <var>PUT</var> and <var>GET</var> arguments.
<br></td></tr><tr align="left"><td valign="top" width="15%"><var>PUT</var> </td><td valign="top" width="70%">(Optional) Shall be an array of type default
<code>INTEGER</code> and rank one. It is <code>INTENT(IN)</code> and the size of
the array must be larger than or equal to the number returned by the
<var>SIZE</var> argument.
<br></td></tr><tr align="left"><td valign="top" width="15%"><var>GET</var> </td><td valign="top" width="70%">(Optional) Shall be an array of type default
<code>INTEGER</code> and rank one. It is <code>INTENT(OUT)</code> and the size
of the array must be larger than or equal to the number returned by
the <var>SIZE</var> argument.
<br></td></tr></table>
<br><dt><em>Example</em>:<dd>
<pre class="smallexample"> SUBROUTINE init_random_seed()
INTEGER :: i, n, clock
INTEGER, DIMENSION(:), ALLOCATABLE :: seed
CALL RANDOM_SEED(size = n)
ALLOCATE(seed(n))
CALL SYSTEM_CLOCK(COUNT=clock)
seed = clock + 37 * (/ (i - 1, i = 1, n) /)
CALL RANDOM_SEED(PUT = seed)
DEALLOCATE(seed)
END SUBROUTINE
</pre>
<br><dt><em>See also</em>:<dd><a href="RANDOM_005fNUMBER.html#RANDOM_005fNUMBER">RANDOM_NUMBER</a>
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