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<li>write_restart command</li>
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<div class="section" id="write-restart-command">
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<span id="index-0"></span><h1>write_restart command</h1>
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<div class="section" id="syntax">
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<h2>Syntax</h2>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">write_restart</span> <span class="n">file</span> <span class="n">keyword</span> <span class="n">value</span> <span class="o">...</span>
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</pre></div>
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</div>
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<ul class="simple">
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<li>file = name of file to write restart information to</li>
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<li>zero or more keyword/value pairs may be appended</li>
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<li>keyword = <em>fileper</em> or <em>nfile</em></li>
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</ul>
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<pre class="literal-block">
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<em>fileper</em> arg = Np
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Np = write one file for every this many processors
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<em>nfile</em> arg = Nf
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Nf = write this many files, one from each of Nf processors
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</pre>
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</div>
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<div class="section" id="examples">
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<h2>Examples</h2>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">write_restart</span> <span class="n">restart</span><span class="o">.</span><span class="n">equil</span>
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<span class="n">write_restart</span> <span class="n">restart</span><span class="o">.</span><span class="n">equil</span><span class="o">.</span><span class="n">mpiio</span>
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<span class="n">write_restart</span> <span class="n">poly</span><span class="o">.%.*</span> <span class="n">nfile</span> <span class="mi">10</span>
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</pre></div>
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</div>
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</div>
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<div class="section" id="description">
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<h2>Description</h2>
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<p>Write a binary restart file of the current state of the simulation.</p>
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<p>During a long simulation, the <a class="reference internal" href="restart.html"><span class="doc">restart</span></a> command is
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typically used to output restart files periodically. The
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write_restart command is useful after a minimization or whenever you
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wish to write out a single current restart file.</p>
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<p>Similar to <a class="reference internal" href="dump.html"><span class="doc">dump</span></a> files, the restart filename can contain
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two wild-card characters. If a “*” appears in the filename, it is
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replaced with the current timestep value. If a “%” character appears
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in the filename, then one file is written by each processor and the
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“%” character is replaced with the processor ID from 0 to P-1. An
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additional file with the “%” replaced by “base” is also written, which
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contains global information. For example, the files written for
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filename restart.% would be restart.base, restart.0, restart.1, ...
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restart.P-1. This creates smaller files and can be a fast mode of
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output and subsequent input on parallel machines that support parallel
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I/O. The optional <em>fileper</em> and <em>nfile</em> keywords discussed below can
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alter the number of files written.</p>
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<p>The restart file can also be written in parallel as one large binary
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file via the MPI-IO library, which is part of the MPI standard for
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versions 2.0 and above. Using MPI-IO requires two steps. First,
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build LAMMPS with its MPIIO package installed, e.g.</p>
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<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">mpiio</span> <span class="c1"># installs the MPIIO package</span>
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<span class="n">make</span> <span class="n">g</span><span class="o">++</span> <span class="c1"># build LAMMPS for your platform</span>
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</pre></div>
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</div>
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<p>Second, use a restart filename which contains ”.mpiio”. Note that it
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does not have to end in ”.mpiio”, just contain those characters.
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Unlike MPI-IO dump files, a particular restart file must be both
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written and read using MPI-IO.</p>
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<p>Restart files can be read by a <a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a>
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command to restart a simulation from a particular state. Because the
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file is binary (to enable exact restarts), it may not be readable on
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another machine. In this case, you can use the <a class="reference internal" href="Section_start.html#start-7"><span class="std std-ref">-r command-line switch</span></a> to convert a restart file to a data
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file.</p>
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<div class="admonition note">
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<p class="first admonition-title">Note</p>
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<p class="last">Although the purpose of restart files is to enable restarting a
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simulation from where it left off, not all information about a
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simulation is stored in the file. For example, the list of fixes that
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were specified during the initial run is not stored, which means the
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new input script must specify any fixes you want to use. Even when
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restart information is stored in the file, as it is for some fixes,
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commands may need to be re-specified in the new input script, in order
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to re-use that information. Details are usually given in the
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documentation of the respective command. Also, see the
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<a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a> command for general information about
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what is stored in a restart file.</p>
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</div>
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<hr class="docutils" />
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<p>The optional <em>nfile</em> or <em>fileper</em> keywords can be used in conjunction
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with the “%” wildcard character in the specified restart file name.
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As explained above, the “%” character causes the restart file to be
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written in pieces, one piece for each of P processors. By default P =
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the number of processors the simulation is running on. The <em>nfile</em> or
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<em>fileper</em> keyword can be used to set P to a smaller value, which can
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be more efficient when running on a large number of processors.</p>
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<p>The <em>nfile</em> keyword sets P to the specified Nf value. For example, if
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Nf = 4, and the simulation is running on 100 processors, 4 files will
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be written, by processors 0,25,50,75. Each will collect information
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from itself and the next 24 processors and write it to a restart file.</p>
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<p>For the <em>fileper</em> keyword, the specified value of Np means write one
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file for every Np processors. For example, if Np = 4, every 4th
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processor (0,4,8,12,etc) will collect information from itself and the
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next 3 processors and write it to a restart file.</p>
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</div>
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<hr class="docutils" />
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<div class="section" id="restrictions">
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<h2>Restrictions</h2>
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<p>This command requires inter-processor communication to migrate atoms
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before the restart file is written. This means that your system must
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be ready to perform a simulation before using this command (force
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fields setup, atom masses initialized, etc).</p>
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<p>To write and read restart files in parallel with MPI-IO, the MPIIO
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package must be installed.</p>
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</div>
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<div class="section" id="related-commands">
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<h2>Related commands</h2>
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<p><a class="reference internal" href="restart.html"><span class="doc">restart</span></a>, <a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a>,
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<a class="reference internal" href="write_data.html"><span class="doc">write_data</span></a></p>
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<p><strong>Default:</strong> none</p>
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