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  25 <div class="refentry">
  26 <a name="boost.compute.accumulate"></a><div class="titlepage"></div>
  27 <div class="refnamediv">
  28 <h2><span class="refentrytitle">Function accumulate</span></h2>
  29 <p>boost::compute::accumulate</p>
  30 </div>
  31 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
  32 <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../boost_compute/reference.html#header.boost.compute.algorithm.accumulate_hpp" title="Header &lt;boost/compute/algorithm/accumulate.hpp&gt;">boost/compute/algorithm/accumulate.hpp</a>&gt;
  33
  34 </span>
  35 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> InputIterator<span class="special">,</span> <span class="keyword">typename</span> T<span class="special">,</span> <span class="keyword">typename</span> BinaryFunction<span class="special">&gt;</span>
  36   <span class="identifier">T</span> <span class="identifier">accumulate</span><span class="special">(</span><span class="identifier">InputIterator</span> first<span class="special">,</span> <span class="identifier">InputIterator</span> last<span class="special">,</span> <span class="identifier">T</span> init<span class="special">,</span>
  37                <span class="identifier">BinaryFunction</span> function<span class="special">,</span>
  38                <span class="identifier">command_queue</span> <span class="special">&amp;</span> queue <span class="special">=</span> <span class="identifier">system</span><span class="special">::</span><span class="identifier">default_queue</span><span class="special">(</span><span class="special">)</span><span class="special">)</span><span class="special">;</span>
  39 <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> InputIterator<span class="special">,</span> <span class="keyword">typename</span> T<span class="special">&gt;</span>
  40   <span class="identifier">T</span> <span class="identifier">accumulate</span><span class="special">(</span><span class="identifier">InputIterator</span> first<span class="special">,</span> <span class="identifier">InputIterator</span> last<span class="special">,</span> <span class="identifier">T</span> init<span class="special">,</span>
  41                <span class="identifier">command_queue</span> <span class="special">&amp;</span> queue <span class="special">=</span> <span class="identifier">system</span><span class="special">::</span><span class="identifier">default_queue</span><span class="special">(</span><span class="special">)</span><span class="special">)</span><span class="special">;</span></pre></div>
  42 <div class="refsect1">
  43 <a name="idp78534432"></a><h2>Description</h2>
  44 <p>Returns the result of applying <code class="computeroutput">function</code> to the elements in the range [<code class="computeroutput">first</code>, <code class="computeroutput">last</code>) and <code class="computeroutput">init</code>.</p>
  45 <p>If no function is specified, <code class="computeroutput">plus</code> will be used.</p>
  46 <p>
  47
  48 In specific situations the call to <code class="computeroutput">accumulate()</code> can be automatically optimized to a call to the more efficient <code class="computeroutput">reduce()</code> algorithm. This occurs when the binary reduction function is recognized as associative (such as the <code class="computeroutput">plus&lt;int&gt;</code> function).</p>
  49 <p>Note that because floating-point addition is not associative, calling <code class="computeroutput">accumulate()</code> with <code class="computeroutput">plus&lt;float&gt;</code> results in a less efficient serial reduction algorithm being executed. If a slight loss in precision is acceptable, the more efficient parallel <code class="computeroutput">reduce()</code> algorithm should be used instead.</p>
  50 <p>For example: </p>
  51 <pre class="programlisting"><span class="comment">// with vec = boost::compute::vector&lt;int&gt;</span>
  52 <span class="identifier">accumulate</span><span class="special">(</span><span class="identifier">vec</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(</span><span class="special">)</span><span class="special">,</span> <span class="identifier">vec</span><span class="special">.</span><span class="identifier">end</span><span class="special">(</span><span class="special">)</span><span class="special">,</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">plus</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span><span class="special">(</span><span class="special">)</span><span class="special">)</span><span class="special">;</span>   <span class="comment">// fast</span>
  53 <span class="identifier">reduce</span><span class="special">(</span><span class="identifier">vec</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(</span><span class="special">)</span><span class="special">,</span> <span class="identifier">vec</span><span class="special">.</span><span class="identifier">end</span><span class="special">(</span><span class="special">)</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">result</span><span class="special">,</span> <span class="identifier">plus</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span><span class="special">(</span><span class="special">)</span><span class="special">)</span><span class="special">;</span> <span class="comment">// fast</span>
  54
  55 <span class="comment">// with vec = boost::compute::vector&lt;float&gt;</span>
  56 <span class="identifier">accumulate</span><span class="special">(</span><span class="identifier">vec</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(</span><span class="special">)</span><span class="special">,</span> <span class="identifier">vec</span><span class="special">.</span><span class="identifier">end</span><span class="special">(</span><span class="special">)</span><span class="special">,</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">plus</span><span class="special">&lt;</span><span class="keyword">float</span><span class="special">&gt;</span><span class="special">(</span><span class="special">)</span><span class="special">)</span><span class="special">;</span>   <span class="comment">// slow</span>
  57 <span class="identifier">reduce</span><span class="special">(</span><span class="identifier">vec</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(</span><span class="special">)</span><span class="special">,</span> <span class="identifier">vec</span><span class="special">.</span><span class="identifier">end</span><span class="special">(</span><span class="special">)</span><span class="special">,</span> <span class="special">&amp;</span><span class="identifier">result</span><span class="special">,</span> <span class="identifier">plus</span><span class="special">&lt;</span><span class="keyword">float</span><span class="special">&gt;</span><span class="special">(</span><span class="special">)</span><span class="special">)</span><span class="special">;</span> <span class="comment">// fast</span>
  58 </pre>
  59 <p>Space complexity: (1)<br>
  60  Space complexity when optimized to <code class="computeroutput">reduce()</code>: (n)</p>
  61 <p><span class="bold"><strong>See Also:</strong></span></p>
  62 <p>reduce() </p>
  63 <p>
  64 </p>
  65 <div class="variablelist"><table border="0" class="variablelist compact">
  66 <colgroup>
  67 <col align="left" valign="top">
  68 <col>
  69 </colgroup>
  70 <tbody>
  71 <tr>
  72 <td><p><span class="term">Parameters:</span></p></td>
  73 <td><div class="variablelist"><table border="0" class="variablelist compact">
  74 <colgroup>
  75 <col align="left" valign="top">
  76 <col>
  77 </colgroup>
  78 <tbody>
  79 <tr>
  80 <td><p><span class="term"><code class="computeroutput">first</code></span></p></td>
  81 <td><p>first element in the input range </p></td>
  82 </tr>
  83 <tr>
  84 <td><p><span class="term"><code class="computeroutput">function</code></span></p></td>
  85 <td><p>binary reduction function </p></td>
  86 </tr>
  87 <tr>
  88 <td><p><span class="term"><code class="computeroutput">init</code></span></p></td>
  89 <td><p>initial value </p></td>
  90 </tr>
  91 <tr>
  92 <td><p><span class="term"><code class="computeroutput">last</code></span></p></td>
  93 <td><p>last element in the input range </p></td>
  94 </tr>
  95 <tr>
  96 <td><p><span class="term"><code class="computeroutput">queue</code></span></p></td>
  97 <td><p>command queue to perform the operation</p></td>
  98 </tr>
  99 </tbody>
 100 </table></div></td>
 101 </tr>
 102 <tr>
 103 <td><p><span class="term">Returns:</span></p></td>
 104 <td><p>the accumulated result value</p></td>
 105 </tr>
 106 </tbody>
 107 </table></div>
 108 </div>
 109 </div>
 110 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 111 <td align="left"></td>
 112 <td align="right"><div class="copyright-footer">Copyright &#169; 2013, 2014 Kyle Lutz<p>
 113         Distributed under the Boost Software License, Version 1.0. (See accompanying
 114         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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