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<li class="toctree-l1"><a class="reference internal" href="Section_intro.html">1. Introduction</a></li>
<li class="toctree-l1"><a class="reference internal" href="Section_start.html">2. Getting Started</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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<li class="toctree-l1"><a class="reference internal" href="Section_perf.html">8. Performance &amp; scalability</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. More details
follow.</p>
<div class="highlight-python"><div class="highlight"><pre>make yes-opt
make mpi # build with the OPT package
Make.py -v -p opt -o mpi -a file mpi # or one-line build via Make.py
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre>lmp_mpi -sf opt -in in.script # run in serial
mpirun -np 4 lmp_mpi -sf opt -in in.script # run in parallel
</pre></div>
</div>
<p><strong>Required hardware/software:</strong></p>
<p>None.</p>
<p><strong>Building LAMMPS with the OPT package:</strong></p>
<p>The lines above illustrate how to build LAMMPS with the OPT package in
two steps, using the &#8220;make&#8221; command. Or how to do it with one command
via 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.</p>
<p>Note that if you use an Intel compiler to build with the OPT package,
the CCFLAGS setting in your Makefile.machine must include &#8220;-restrict&#8221;.
The Make.py command will add this automatically.</p>
<p><strong>Run with the OPT package from the command line:</strong></p>
<p>As in the lines above, 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>
<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>
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<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>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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