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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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<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"><span class="doc">Return to Section accelerate overview</span></a></p>
<div class="section" id="opt-package">
<h1>5.OPT package</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-default"><div class="highlight"><pre><span></span><span class="n">make</span> <span class="n">yes</span><span class="o">-</span><span class="n">opt</span>
<span class="n">make</span> <span class="n">mpi</span> <span class="c1"># build with the OPT package</span>
<span class="n">Make</span><span class="o">.</span><span class="n">py</span> <span class="o">-</span><span class="n">v</span> <span class="o">-</span><span class="n">p</span> <span class="n">opt</span> <span class="o">-</span><span class="n">o</span> <span class="n">mpi</span> <span class="o">-</span><span class="n">a</span> <span class="n">file</span> <span class="n">mpi</span> <span class="c1"># or one-line build via Make.py</span>
</pre></div>
</div>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">lmp_mpi</span> <span class="o">-</span><span class="n">sf</span> <span class="n">opt</span> <span class="o">-</span><span class="ow">in</span> <span class="ow">in</span><span class="o">.</span><span class="n">script</span> <span class="c1"># run in serial</span>
<span class="n">mpirun</span> <span class="o">-</span><span class="n">np</span> <span class="mi">4</span> <span class="n">lmp_mpi</span> <span class="o">-</span><span class="n">sf</span> <span class="n">opt</span> <span class="o">-</span><span class="ow">in</span> <span class="ow">in</span><span class="o">.</span><span class="n">script</span> <span class="c1"># run in parallel</span>
</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 class="std std-ref">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 class="std std-ref">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"><span class="doc">suffix opt</span></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-default"><div class="highlight"><pre><span></span><span class="n">pair_style</span> <span class="n">lj</span><span class="o">/</span><span class="n">cut</span><span class="o">/</span><span class="n">opt</span> <span class="mf">2.5</span>
</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>Just try out an OPT pair style to see how it performs.</p>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<p>None.</p>
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