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<h4 class="subsectionHead"><span class="titlemark">7.11 </span> <a
id="x79-1160007.11"></a>psb_max &#8212; Global maximum</h4>
<pre class="verbatim" id="verbatim-71">
call&#x00A0;psb_max(ctxt,&#x00A0;dat,&#x00A0;root)
</pre>
<!--l. 383--><p class="nopar" >
<!--l. 385--><p class="indent" > This subroutine implements a maximum valuereduction operation based on the
underlying communication library.
<dl class="description"><dt class="description">
<span
class="cmbx-10">Type:</span> </dt><dd
class="description">Synchronous.
</dd><dt class="description">
<span
class="cmbx-10">On Entry</span> </dt><dd
class="description">
</dd><dt class="description">
<span
class="cmbx-10">ctxt</span> </dt><dd
class="description">the communication context identifying the virtual parallel machine.<br
class="newline" />Scope: <span
class="cmbx-10">global</span>.<br
class="newline" />Type: <span
class="cmbx-10">required</span>.<br
class="newline" />Intent: <span
class="cmbx-10">in</span>.<br
class="newline" />Specified as: an integer variable.
</dd><dt class="description">
<span
class="cmbx-10">dat</span> </dt><dd
class="description">The local contribution to the global maximum.<br
class="newline" />Scope: <span
class="cmbx-10">local</span>.<br
class="newline" />Type: <span
class="cmbx-10">required</span>.<br
class="newline" />Intent: <span
class="cmbx-10">inout</span>.<br
class="newline" />Specified as: an integer or real variable, which may be a scalar, or a rank
1 or 2 array. &#x00A0;Type, kind, rank and size must agree on all processes.
</dd><dt class="description">
<span
class="cmbx-10">root</span> </dt><dd
class="description">Process to hold the final maximum, or <span
class="cmsy-10">-</span>1 to make it available on all
processes.<br
class="newline" />Scope: <span
class="cmbx-10">global</span>.<br
class="newline" />Type: <span
class="cmbx-10">optional</span>.<br
class="newline" />Intent: <span
class="cmbx-10">in</span>.<br
class="newline" />Specified as: an integer value <span
class="cmsy-10">-</span>1 <span
class="cmmi-10">&#x003C;</span>= <span
class="cmmi-10">root &#x003C;</span>= <span
class="cmmi-10">np </span><span
class="cmsy-10">- </span>1, default -1. <br
class="newline" /></dd></dl>
<!--l. 412--><p class="indent" >
<dl class="description"><dt class="description">
<span
class="cmbx-10">On Return</span> </dt><dd
class="description">
</dd><dt class="description">
<span
class="cmbx-10">dat</span> </dt><dd
class="description">On destination process(es), the result of the maximum operation.<br
class="newline" />Scope: <span
class="cmbx-10">global</span>.<br
class="newline" />Type: <span
class="cmbx-10">required</span>.<br
class="newline" />Intent: <span
class="cmbx-10">in</span>.<br
class="newline" />Specified as: an integer or real variable, which may be a scalar, or a rank
1 or 2 array. &#x00A0;Type, kind, rank and size must agree on all processes.</dd></dl>
<!--l. 424--><p class="noindent" ><span
class="cmbx-12">Notes</span>
<ol class="enumerate1" >
<li
class="enumerate" id="x79-116002x1">The <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">dat</span></span></span> argument is both input and output, and its value may be changed
even on processes different from the final result destination.
</li>
<li
class="enumerate" id="x79-116004x2">The <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">dat</span></span></span> argument may also be a long integer scalar.</li></ol>
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