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<title>5.OPT package &mdash; LAMMPS 15 May 2015 version documentation</title>
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<li class="toctree-l1"><a class="reference internal" href="Section_intro.html">1. Introduction</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Section_accelerate.html">5. Accelerating LAMMPS performance</a></li>
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<p><a class="reference internal" href="Section_accelerate.html"><em>Return to Section accelerate overview</em></a></p>
<div class="section" id="opt-package">
<h1>5.OPT package<a class="headerlink" href="#opt-package" title="Permalink to this headline"></a></h1>
<p>The OPT package was developed by James Fischer (High Performance
Technologies), David Richie, and Vincent Natoli (Stone Ridge
Technologies). It contains a handful of pair styles whose compute()
methods were rewritten in C++ templated form to reduce the overhead
due to if tests and other conditional code.</p>
<p>Here is a quick overview of how to use the OPT package:</p>
<ul class="simple">
<li>include the OPT package and build LAMMPS</li>
<li>use OPT pair styles in your input script</li>
</ul>
<p>The last step can be done using the &#8220;-sf opt&#8221; <a class="reference internal" href="Section_start.html#start-7"><span>command-line switch</span></a>. Or the effect of the &#8220;-sf&#8221; switch
can be duplicated by adding a <a class="reference internal" href="suffix.html"><em>suffix opt</em></a> command to your
input script.</p>
<p><strong>Required hardware/software:</strong></p>
<p>None.</p>
<p><strong>Building LAMMPS with the OPT package:</strong></p>
<p>Include the package and build LAMMPS:</p>
<p>To do this in one line, use the src/Make.py script, described in
<a class="reference internal" href="Section_start.html#start-4"><span>Section 2.4</span></a> of the manual. Type &#8220;Make.py
-h&#8221; for help. If run from the src directory, this command will create
src/lmp_opt using src/MAKE/Makefile.mpi as the starting
Makefile.machine:</p>
<div class="highlight-python"><div class="highlight"><pre>Make.py -p opt -o opt file mpi
</pre></div>
</div>
<p>Or you can follow these steps:</p>
<div class="highlight-python"><div class="highlight"><pre>cd lammps/src
make yes-opt
make machine
</pre></div>
</div>
<p>If you are using Intel compilers, then the CCFLAGS setting in
Makefile.machine needs to include &#8220;-restrict&#8221;.</p>
<p><strong>Run with the OPT package from the command line:</strong></p>
<p>Use the &#8220;-sf opt&#8221; <a class="reference internal" href="Section_start.html#start-7"><span>command-line switch</span></a>,
which will automatically append &#8220;opt&#8221; to styles that support it.</p>
<div class="highlight-python"><div class="highlight"><pre>lmp_machine -sf opt -in in.script
mpirun -np 4 lmp_machine -sf opt -in in.script
</pre></div>
</div>
<p><strong>Or run with the OPT package by editing an input script:</strong></p>
<p>Use the <a class="reference internal" href="suffix.html"><em>suffix opt</em></a> command, or you can explicitly add an
&#8220;opt&#8221; suffix to individual styles in your input script, e.g.</p>
<div class="highlight-python"><div class="highlight"><pre>pair_style lj/cut/opt 2.5
</pre></div>
</div>
<p><strong>Speed-ups to expect:</strong></p>
<p>You should see a reduction in the &#8220;Pair time&#8221; value printed at the end
of a run. On most machines for reasonable problem sizes, it will be a
5 to 20% savings.</p>
<p><strong>Guidelines for best performance:</strong></p>
<p>None. Just try out an OPT pair style to see how it performs.</p>
<div class="section" id="restrictions">
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline"></a></h2>
<p>None.</p>
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