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<h4 class="subsectionHead"><span class="titlemark">7.10 </span> <a
id="x78-1150007.10"></a>psb_sum &#8212; Global sum</h4>
<pre class="verbatim" id="verbatim-70">
call&#x00A0;psb_sum(ctxt,&#x00A0;dat&#x00A0;[,&#x00A0;root,&#x00A0;mode,&#x00A0;request])
</pre>
<!--l. 349--><p class="nopar" >
<!--l. 351--><p class="indent" > This subroutine implements a sum reduction 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 sum.<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">inout</span>.<br
class="newline" />Specified as: an integer, real or complex 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 sum, 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. &#x00A0;
</dd><dt class="description">
<span
class="cmbx-10">mode</span> </dt><dd
class="description">Whether the call is started in non-blocking mode and completed later,
or is executed synchronously.<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, with the value determined by the bitwise OR of
<span class="obeylines-h"><span class="verb"><span
class="cmtt-10">psb_collective_start_</span></span></span>, <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">psb_collective_end_</span></span></span>. Default: both fields are
selected (i.e. require synchronous completion).<br
class="newline" />
</dd><dt class="description">
<span
class="cmbx-10">request</span> </dt><dd
class="description">A request variable to check for operation completion.<br
class="newline" />Scope: <span
class="cmbx-10">local</span>.<br
class="newline" />Type: <span
class="cmbx-10">optional</span>.<br
class="newline" />Intent: <span
class="cmbx-10">inout</span>.<br
class="newline" />If <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">mode</span></span></span> does not specify synchronous completion, then this variable must
be present.</dd></dl>
<!--l. 392--><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 sum 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">inout</span>.<br
class="newline" />Specified as: an integer, real or complex variable, which may be a scalar,
or a rank 1 or 2 array. <br
class="newline" />Type, kind, rank and size must agree on all processes.
</dd><dt class="description">
<span
class="cmbx-10">request</span> </dt><dd
class="description">A request variable to check for operation completion.<br
class="newline" />Scope: <span
class="cmbx-10">local</span>.<br
class="newline" />Type: <span
class="cmbx-10">optional</span>.<br
class="newline" />Intent: <span
class="cmbx-10">inout</span>.<br
class="newline" />If <span class="obeylines-h"><span class="verb"><span
class="cmtt-10">mode</span></span></span> does not specify synchronous completion, then this variable must
be present.</dd></dl>
<!--l. 409--><p class="noindent" ><span
class="cmbx-12">Notes</span>
<ol class="enumerate1" >
<li
class="enumerate" id="x78-115002x1">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="x78-115004x2">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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