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<title>The GNU Fortran Compiler: CO_REDUCE</title>
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<a name="CO_005fREDUCE"></a>
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<p>
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Next: <a href="CO_005fSUM.html#CO_005fSUM" accesskey="n" rel="next">CO_SUM</a>, Previous: <a href="CO_005fMIN.html#CO_005fMIN" accesskey="p" rel="prev">CO_MIN</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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<a name="CO_005fREDUCE-_002d_002d_002d-Reduction-of-values-on-the-current-set-of-images"></a>
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<h3 class="section">9.62 <code>CO_REDUCE</code> — Reduction of values on the current set of images</h3>
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<a name="index-CO_005fREDUCE"></a>
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<a name="index-Collectives_002c-generic-reduction"></a>
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<dl compact="compact">
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<dt><em>Description</em>:</dt>
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<dd><p><code>CO_REDUCE</code> determines element-wise the reduction of the value of <var>A</var>
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on all images of the current team. The pure function passed as <var>OPERATOR</var>
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is used to pairwise reduce the values of <var>A</var> by passing either the value
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of <var>A</var> of different images or the result values of such a reduction as
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argument. If <var>A</var> is an array, the deduction is done element wise. If
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<var>RESULT_IMAGE</var> is present, the result values are returned in <var>A</var> on
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the specified image only and the value of <var>A</var> on the other images become
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undefined. If <var>RESULT_IMAGE</var> is not present, the value is returned on all
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images. If the execution was successful and <var>STAT</var> is present, it is
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assigned the value zero. If the execution failed, <var>STAT</var> gets assigned
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a nonzero value and, if present, <var>ERRMSG</var> gets assigned a value describing
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the occurred error.
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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>Technical Specification (TS) 18508 or 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>Collective 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>CALL CO_REDUCE(A, OPERATOR, [, RESULT_IMAGE, STAT, ERRMSG])</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>A</var></td><td width="70%">is an <code>INTENT(INOUT)</code> argument and shall be
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nonpolymorphic. If it is allocatable, it shall be allocated; if it is a pointer,
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it shall be associated. <var>A</var> shall have the same type and type parameters on
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all images of the team; if it is an array, it shall have the same shape on all
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images.</td></tr>
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<tr><td width="15%"><var>OPERATOR</var></td><td width="70%">pure function with two scalar nonallocatable
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arguments, which shall be nonpolymorphic and have the same type and type
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parameters as <var>A</var>. The function shall return a nonallocatable scalar of
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the same type and type parameters as <var>A</var>. The function shall be the same on
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all images and with regards to the arguments mathematically commutative and
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associative. Note that <var>OPERATOR</var> may not be an elemental function, unless
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it is an intrisic function.</td></tr>
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<tr><td width="15%"><var>RESULT_IMAGE</var></td><td width="70%">(optional) a scalar integer expression; if
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present, it shall have the same the same value on all images and refer to an
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image of the current team.</td></tr>
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<tr><td width="15%"><var>STAT</var></td><td width="70%">(optional) a scalar integer variable</td></tr>
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<tr><td width="15%"><var>ERRMSG</var></td><td width="70%">(optional) a scalar character variable</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
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integer :: val
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val = this_image ()
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call co_reduce (val, result_image=1, operator=myprod)
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if (this_image() == 1) then
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write(*,*) "Product value", val ! prints num_images() factorial
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end if
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contains
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pure function myprod(a, b)
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integer, value :: a, b
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integer :: myprod
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myprod = a * b
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end function myprod
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end program test
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</pre></div>
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</dd>
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<dt><em>Note</em>:</dt>
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<dd><p>While the rules permit in principle an intrinsic function, none of the
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intrinsics in the standard fulfill the criteria of having a specific
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function, which takes two arguments of the same type and returning that
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type as result.
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</p>
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</dd>
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<dt><em>See also</em>:</dt>
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<dd><p><a href="CO_005fMIN.html#CO_005fMIN">CO_MIN</a>, <a href="CO_005fMAX.html#CO_005fMAX">CO_MAX</a>, <a href="CO_005fSUM.html#CO_005fSUM">CO_SUM</a>, <a href="CO_005fBROADCAST.html#CO_005fBROADCAST">CO_BROADCAST</a>
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</p></dd>
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</dl>
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Next: <a href="CO_005fSUM.html#CO_005fSUM" accesskey="n" rel="next">CO_SUM</a>, Previous: <a href="CO_005fMIN.html#CO_005fMIN" accesskey="p" rel="prev">CO_MIN</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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