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<title>Map (parallel pattern)</title>
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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Map (parallel pattern)</span></span>
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<div id="mw-content-text" class="mw-body-content mw-content-ltr" lang="en" dir="ltr"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><p><b>Map</b> is an <a href="Programming_idiom" title="Programming idiom">idiom</a> in <a href="Parallel_computing" title="Parallel computing">parallel computing</a> where a simple operation is applied to all elements of a sequence, potentially in parallel.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> It is used to solve <a href="Embarrassingly_parallel" title="Embarrassingly parallel">embarrassingly parallel</a> problems: those problems that can be decomposed into independent subtasks, requiring no communication/synchronization between the subtasks except a <a href="Fork%E2%80%93join_model" title="Fork–join model">join</a> or <a href="Barrier_(computer_science)" title="Barrier (computer science)">barrier</a> at the end.
</p><p>When applying the map pattern, one formulates an <i>elemental function</i> that captures the operation to be performed on a data item that represents a part of the problem, then applies this elemental function in one or more <a href="Thread_(computing)" title="Thread (computing)">threads of execution</a>, <a href="Hyperthread" class="mw-redirect" title="Hyperthread">hyperthreads</a>, <a href="SIMD_lanes" class="mw-redirect" title="SIMD lanes">SIMD lanes</a> or on <a href="Distributed_computing" title="Distributed computing">multiple computers</a>.
</p><p>Some parallel programming systems, such as <a href="OpenMP" title="OpenMP">OpenMP</a> and <a href="Cilk" title="Cilk">Cilk</a>, have language support for the map pattern in the form of a <b>parallel for loop</b>;<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> languages such as <a href="OpenCL" title="OpenCL">OpenCL</a> and <a href="CUDA" title="CUDA">CUDA</a> support elemental functions (as "<a href="Compute_kernel" title="Compute kernel">kernels</a>") at the language level. The map pattern is typically combined with other parallel design patterns. For example, map combined with category reduction gives the <a href="MapReduce" title="MapReduce">MapReduce</a> pattern.<sup id="cite_ref-spp_3-0" class="reference"><a href="#cite_note-spp-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Pages: 106–107">: 106–107 </span></sup>
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<div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2></div>
<ul><li><a href="Map_(higher-order_function)" title="Map (higher-order function)">Map (higher-order function)</a></li>
<li><a href="Functional_programming" title="Functional programming">Functional programming</a></li>
<li><a href="Algorithmic_skeleton" title="Algorithmic skeleton">Algorithmic skeleton</a></li></ul>
<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>
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<li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">
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</style><cite id="CITEREFSamadiJamshidiLeeMahlke2014" class="citation conference cs1">Samadi, Mehrzad; Jamshidi, Davoud Anoushe; Lee, Janghaeng; Mahlke, Scott (2014). <a rel="nofollow" class="external text" href="http://cccp.eecs.umich.edu/papers/samadi-asplos14.pdf"><i>Paraprox: Pattern-based approximation for data parallel applications</i></a> <span class="cs1-format">(PDF)</span>. Proc. 19th Int'l Conf. on Architectural support for programming languages and operating systems. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1145%2F2541940.2541948">10.1145/2541940.2541948</a>.</cite></span>
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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><cite id="CITEREFWolfe2015" class="citation web cs1">Wolfe, Michael (6 April 2015). <a rel="nofollow" class="external text" href="http://www.hpcwire.com/2015/04/06/compilers-and-more-the-past-present-and-future-of-parallel-loops/">"Compilers and More: The Past, Present and Future of Parallel Loops"</a>. <i>HPCwire</i>.</cite></span>
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<li id="cite_note-spp-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-spp_3-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFMichael_McCoolJames_ReindersArch_Robison2013" class="citation book cs1">Michael McCool; James Reinders; Arch Robison (2013). <i>Structured Parallel Programming: Patterns for Efficient Computation</i>. Elsevier. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0124159938</bdi>.</cite></span>
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