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<h4 class="subsectionHead"><span class="titlemark">7.11 </span> <a
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id="x79-1160007.11"></a>psb_max — Global maximum</h4>
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<pre class="verbatim" id="verbatim-75">
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call psb_max(ctxt, dat [, root, mode, request])
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</pre>
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<!--l. 512--><p class="nopar" >
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<!--l. 514--><p class="indent" > This subroutine implements a maximum valuereduction operation based on the
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underlying communication library.
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<dl class="description"><dt class="description">
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<span
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class="cmbx-10">Type:</span> </dt><dd
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class="description">Synchronous.
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</dd><dt class="description">
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<span
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class="cmbx-10">On Entry</span> </dt><dd
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class="description">
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</dd><dt class="description">
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<span
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class="cmbx-10">ctxt</span> </dt><dd
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class="description">the communication context identifying the virtual parallel machine.<br
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class="newline" />Scope: <span
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class="cmbx-10">global</span>.<br
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class="newline" />Type: <span
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class="cmbx-10">required</span>.<br
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class="newline" />Intent: <span
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class="cmbx-10">in</span>.<br
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class="newline" />Specified as: an integer variable.
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</dd><dt class="description">
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<span
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class="cmbx-10">dat</span> </dt><dd
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class="description">The local contribution to the global maximum.<br
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class="newline" />Scope: <span
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class="cmbx-10">local</span>.<br
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class="newline" />Type: <span
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class="cmbx-10">required</span>.<br
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class="newline" />Intent: <span
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class="cmbx-10">inout</span>.<br
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class="newline" />Specified as: an integer or real variable, which may be a scalar, or a rank
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1 or 2 array.  Type, kind, rank and size must agree on all processes.
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</dd><dt class="description">
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<span
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class="cmbx-10">root</span> </dt><dd
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class="description">Process to hold the final maximum, or <span
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class="cmsy-10">-</span>1 to make it available on all
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processes.<br
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class="newline" />Scope: <span
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class="cmbx-10">global</span>.<br
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class="newline" />Type: <span
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class="cmbx-10">optional</span>.<br
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class="newline" />Intent: <span
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class="cmbx-10">in</span>.<br
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class="newline" />Specified as: an integer value <span
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class="cmsy-10">-</span>1 <span
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class="cmmi-10"><</span>= <span
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class="cmmi-10">root <</span>= <span
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class="cmmi-10">np </span><span
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class="cmsy-10">- </span>1, default -1. <br
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class="newline" />
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</dd><dt class="description">
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<span
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class="cmbx-10">mode</span> </dt><dd
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class="description">Whether the call is started in non-blocking mode and completed later,
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or is executed synchronously.<br
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class="newline" />Scope: <span
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class="cmbx-10">global</span>.<br
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class="newline" />Type: <span
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class="cmbx-10">optional</span>.<br
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class="newline" />Intent: <span
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class="cmbx-10">in</span>.<br
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class="newline" />Specified as: an integer value. The action to be taken is determined by
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its bit fields, which can be set with bitwise <span class="obeylines-h"><span class="verb"><span
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class="cmtt-10">OR</span></span></span>. Basic action values are
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<span class="obeylines-h"><span class="verb"><span
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class="cmtt-10">psb_collective_start_</span></span></span>, <span class="obeylines-h"><span class="verb"><span
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class="cmtt-10">psb_collective_end_</span></span></span>. Default: both fields are
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selected (i.e. require synchronous completion).<br
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class="newline" />
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</dd><dt class="description">
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<span
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class="cmbx-10">request</span> </dt><dd
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class="description">A request variable to check for operation completion.<br
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class="newline" />Scope: <span
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class="cmbx-10">local</span>.<br
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class="newline" />Type: <span
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class="cmbx-10">optional</span>.<br
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class="newline" />Intent: <span
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class="cmbx-10">inout</span>.<br
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class="newline" />If <span class="obeylines-h"><span class="verb"><span
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class="cmtt-10">mode</span></span></span> does not specify synchronous completion, then this variable must
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be present.</dd></dl>
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<!--l. 556--><p class="indent" >
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<dl class="description"><dt class="description">
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<span
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class="cmbx-10">On Return</span> </dt><dd
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class="description">
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</dd><dt class="description">
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<span
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class="cmbx-10">dat</span> </dt><dd
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class="description">On destination process(es), the result of the maximum operation.<br
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class="newline" />Scope: <span
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class="cmbx-10">global</span>.<br
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class="newline" />Type: <span
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class="cmbx-10">required</span>.<br
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class="newline" />Intent: <span
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class="cmbx-10">in</span>.<br
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class="newline" />Specified as: an integer or real variable, which may be a scalar, or a rank
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1 or 2 array.  Type, kind, rank and size must agree on all processes.
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</dd><dt class="description">
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<span
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class="cmbx-10">request</span> </dt><dd
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class="description">A request variable to check for operation completion.<br
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class="newline" />Scope: <span
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class="cmbx-10">local</span>.<br
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class="newline" />Type: <span
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class="cmbx-10">optional</span>.<br
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class="newline" />Intent: <span
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class="cmbx-10">inout</span>.<br
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class="newline" />If <span class="obeylines-h"><span class="verb"><span
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class="cmtt-10">mode</span></span></span> does not specify synchronous completion, then this variable must
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be present.</dd></dl>
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<!--l. 574--><p class="noindent" ><span
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class="cmbx-12">Notes</span>
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<ol class="enumerate1" >
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<li
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class="enumerate" id="x79-116002x1">The <span class="obeylines-h"><span class="verb"><span
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class="cmtt-10">dat</span></span></span> argument is both input and output, and its value may be changed
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even on processes different from the final result destination.
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</li>
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<li
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class="enumerate" id="x79-116004x2">The <span class="obeylines-h"><span class="verb"><span
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class="cmtt-10">mode</span></span></span> argument can be built with the bitwise <span class="obeylines-h"><span class="verb"><span
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class="cmtt-10">IOR()</span></span></span> operator; in the
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following example, the argument is forcing immediate completion, hence the
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<span class="obeylines-h"><span class="verb"><span
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class="cmtt-10">request</span></span></span> argument needs not be specified:
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<div class="center"
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>
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<!--l. 589--><p class="noindent" >
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<div class="minipage"><pre class="verbatim" id="verbatim-76">
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  call psb_max(ctxt,dat,mode=ior(psb_collective_start_,psb_collective_end_))
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</pre>
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<!--l. 593--><p class="nopar" ></div></div>
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</li>
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<li
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class="enumerate" id="x79-116006x3">When splitting the operation in two calls, the <span class="obeylines-h"><span class="verb"><span
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class="cmtt-10">dat</span></span></span> argument <span
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class="cmti-10">must not </span>be
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accessed between calls:
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<div class="center"
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>
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<!--l. 609--><p class="noindent" >
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<div class="minipage"><pre class="verbatim" id="verbatim-77">
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  call psb_max(ctxt,dat,mode=psb_collective_start_,request=max_request)
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  ....... ! Do not access dat
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  call psb_max(ctxt,dat,mode=psb_collective_end_,request=max_request)
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</pre>
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<!--l. 615--><p class="nopar" ></div></div>
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</li></ol>
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<!--l. 621--><div class="crosslinks"><p class="noindent">[<a
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href="userhtmlsu71.html" >next</a>] [<a
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href="userhtmlsu66.html" >prev</a>] [<a
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href="userhtmlsu66.html#tailuserhtmlsu66.html" >prev-tail</a>] [<a
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href="userhtmlsu67.html" >front</a>] [<a
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href="userhtmlsu59.html#userhtmlsu70.html" >up</a>] </p></div>
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