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<div class="refentry">
<a name="boost.mpi.gather"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Function gather</span></h2>
<p>boost::mpi::gather — Gather the values stored at every process into a vector at the root process. </p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: <<a class="link" href="../../mpi/reference.html#header.boost.mpi.collectives_hpp" title="Header <boost/mpi/collectives.hpp>">boost/mpi/collectives.hpp</a>>
</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span>
<span class="keyword">void</span> <span class="identifier">gather</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="communicator.html" title="Class communicator">communicator</a> <span class="special">&</span> comm<span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span> <span class="special">&</span> in_value<span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span> <span class="identifier">T</span> <span class="special">></span> <span class="special">&</span> out_values<span class="special">,</span> <span class="keyword">int</span> root<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span>
<span class="keyword">void</span> <span class="identifier">gather</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="communicator.html" title="Class communicator">communicator</a> <span class="special">&</span> comm<span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span> <span class="special">&</span> in_value<span class="special">,</span> <span class="identifier">T</span> <span class="special">*</span> out_values<span class="special">,</span>
<span class="keyword">int</span> root<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span>
<span class="keyword">void</span> <span class="identifier">gather</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="communicator.html" title="Class communicator">communicator</a> <span class="special">&</span> comm<span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span> <span class="special">&</span> in_value<span class="special">,</span> <span class="keyword">int</span> root<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span>
<span class="keyword">void</span> <span class="identifier">gather</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="communicator.html" title="Class communicator">communicator</a> <span class="special">&</span> comm<span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span> <span class="special">*</span> in_values<span class="special">,</span> <span class="keyword">int</span> n<span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span> <span class="identifier">T</span> <span class="special">></span> <span class="special">&</span> out_values<span class="special">,</span> <span class="keyword">int</span> root<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span>
<span class="keyword">void</span> <span class="identifier">gather</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="communicator.html" title="Class communicator">communicator</a> <span class="special">&</span> comm<span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span> <span class="special">*</span> in_values<span class="special">,</span> <span class="keyword">int</span> n<span class="special">,</span>
<span class="identifier">T</span> <span class="special">*</span> out_values<span class="special">,</span> <span class="keyword">int</span> root<span class="special">)</span><span class="special">;</span>
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span>
<span class="keyword">void</span> <span class="identifier">gather</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="communicator.html" title="Class communicator">communicator</a> <span class="special">&</span> comm<span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span> <span class="special">*</span> in_values<span class="special">,</span> <span class="keyword">int</span> n<span class="special">,</span> <span class="keyword">int</span> root<span class="special">)</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idp160559704"></a><h2>Description</h2>
<p><code class="computeroutput">gather</code> is a collective algorithm that collects the values stored at each process into a vector of values at the <code class="computeroutput">root</code> process. This vector is indexed by the process number that the value came from. The type <code class="computeroutput">T</code> of the values may be any type that is serializable or has an associated MPI data type.</p>
<p>When the type <code class="computeroutput">T</code> has an associated MPI data type, this routine invokes <code class="computeroutput">MPI_Gather</code> to gather the values.</p>
<p>
</p>
<div class="variablelist"><table border="0" class="variablelist compact">
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<td><p><span class="term">Parameters:</span></p></td>
<td><div class="variablelist"><table border="0" class="variablelist compact">
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<td><p><span class="term"><code class="computeroutput">comm</code></span></p></td>
<td><p>The communicator over which the gather will occur.</p></td>
</tr>
<tr>
<td><p><span class="term"><code class="computeroutput">in_value</code></span></p></td>
<td><p>The value to be transmitted by each process. For gathering arrays of values, <code class="computeroutput">in_values</code> points to storage for <code class="computeroutput">n*comm</code>.size() values.</p></td>
</tr>
<tr>
<td><p><span class="term"><code class="computeroutput">out_values</code></span></p></td>
<td><p>A vector or pointer to storage that will be populated with the values from each process, indexed by the process ID number. If it is a vector, it will be resized accordingly. For non-root processes, this parameter may be omitted. If it is still provided, however, it will be unchanged.</p></td>
</tr>
<tr>
<td><p><span class="term"><code class="computeroutput">root</code></span></p></td>
<td><p>The process ID number that will collect the values. This value must be the same on all processes. </p></td>
</tr>
</tbody>
</table></div></td>
</tr></tbody>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="right"><div class="copyright-footer">Copyright © 2005-2007 Douglas Gregor,
Matthias Troyer, Trustees of Indiana University<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">
http://www.boost.org/LICENSE_1_0.txt </a>)
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