1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Function accumulate</title> 5<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../index.html" title="Chapter 1. Boost.Compute"> 8<link rel="up" href="../../boost_compute/reference.html#header.boost.compute.algorithm.accumulate_hpp" title="Header <boost/compute/algorithm/accumulate.hpp>"> 9<link rel="prev" href="../../boost_compute/reference.html" title="Reference"> 10<link rel="next" href="adjacent_difference.html" title="Function adjacent_difference"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="../../boost_compute/reference.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../boost_compute/reference.html#header.boost.compute.algorithm.accumulate_hpp"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="adjacent_difference.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 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: <<a class="link" href="../../boost_compute/reference.html#header.boost.compute.algorithm.accumulate_hpp" title="Header <boost/compute/algorithm/accumulate.hpp>">boost/compute/algorithm/accumulate.hpp</a>> 33 34</span> 35<span class="keyword">template</span><span class="special"><</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">></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">&</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"><</span><span class="keyword">typename</span> InputIterator<span class="special">,</span> <span class="keyword">typename</span> T<span class="special">></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">&</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="idm45849523504512"></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 48In 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<int></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<float></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<int></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"><</span><span class="keyword">int</span><span class="special">></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">&</span><span class="identifier">result</span><span class="special">,</span> <span class="identifier">plus</span><span class="special"><</span><span class="keyword">int</span><span class="special">></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<float></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"><</span><span class="keyword">float</span><span class="special">></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">&</span><span class="identifier">result</span><span class="special">,</span> <span class="identifier">plus</span><span class="special"><</span><span class="keyword">float</span><span class="special">></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: \Omega(1)<br> 60 Space complexity when optimized to <code class="computeroutput">reduce()</code>: \Omega(n)</p> 61<p><span class="bold"><strong>See Also:</strong></span></p> 62<p>reduce() </p> 63<p> 64</p> 65<p> 66</p> 67<div class="variablelist"><table border="0" class="variablelist compact"> 68<colgroup> 69<col align="left" valign="top"> 70<col> 71</colgroup> 72<tbody> 73<tr> 74<td><p><span class="term">Parameters:</span></p></td> 75<td><div class="variablelist"><table border="0" class="variablelist compact"> 76<colgroup> 77<col align="left" valign="top"> 78<col> 79</colgroup> 80<tbody> 81<tr> 82<td><p><span class="term"><code class="computeroutput">first</code></span></p></td> 83<td><p>first element in the input range </p></td> 84</tr> 85<tr> 86<td><p><span class="term"><code class="computeroutput">function</code></span></p></td> 87<td><p>binary reduction function </p></td> 88</tr> 89<tr> 90<td><p><span class="term"><code class="computeroutput">init</code></span></p></td> 91<td><p>initial value </p></td> 92</tr> 93<tr> 94<td><p><span class="term"><code class="computeroutput">last</code></span></p></td> 95<td><p>last element in the input range </p></td> 96</tr> 97<tr> 98<td><p><span class="term"><code class="computeroutput">queue</code></span></p></td> 99<td><p>command queue to perform the operation</p></td> 100</tr> 101</tbody> 102</table></div></td> 103</tr> 104<tr> 105<td><p><span class="term">Returns:</span></p></td> 106<td><p>the accumulated result value</p></td> 107</tr> 108</tbody> 109</table></div> 110</div> 111</div> 112<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 113<td align="left"></td> 114<td align="right"><div class="copyright-footer">Copyright © 2013, 2014 Kyle Lutz<p> 115 Distributed under the Boost Software License, Version 1.0. (See accompanying 116 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>) 117 </p> 118</div></td> 119</tr></table> 120<hr> 121<div class="spirit-nav"> 122<a accesskey="p" href="../../boost_compute/reference.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../boost_compute/reference.html#header.boost.compute.algorithm.accumulate_hpp"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="adjacent_difference.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 123</div> 124</body> 125</html> 126
