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<div class="section" id="fix-lb-momentum-command">
<span id="index-0"></span><h1>fix lb/momentum command<a class="headerlink" href="#fix-lb-momentum-command" title="Permalink to this headline">¶</a></h1>
<div class="section" id="syntax">
<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
<div class="highlight-python"><div class="highlight"><pre>fix ID group-ID lb/momentum nevery keyword values ...
</pre></div>
</div>
<ul class="simple">
<li>ID, group-ID are documented in the <a class="reference internal" href="fix.html"><em>fix</em></a> command</li>
<li>lb/momentum = style name of this fix command</li>
<li>nevery = adjust the momentum every this many timesteps</li>
<li>zero or more keyword/value pairs may be appended</li>
<li>keyword = <em>linear</em></li>
</ul>
<pre class="literal-block">
<em>linear</em> values = xflag yflag zflag
xflag,yflag,zflag = 0/1 to exclude/include each dimension.
</pre>
</div>
<div class="section" id="examples">
<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
<div class="highlight-python"><div class="highlight"><pre>fix 1 sphere lb/momentum
fix 1 all lb/momentum linear 1 1 0
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
<p>This fix is based on the <a class="reference internal" href="fix_momentum.html"><em>fix momentum</em></a> command, and
was created to be used in place of that command, when a
lattice-Boltzmann fluid is present.</p>
<p>Zero the total linear momentum of the system, including both the atoms
specified by group-ID and the lattice-Boltzmann fluid every nevery
timesteps. This is accomplished by adjusting the particle velocities
and the fluid velocities at each lattice site.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">This fix only considers the linear momentum of the system.</p>
</div>
<p>By default, the subtraction is performed for each dimension. This can
be changed by specifying the keyword <em>linear</em>, along with a set of
three flags set to 0/1 in order to exclude/ include the corresponding
dimension.</p>
</div>
<div class="section" id="restart-fix-modify-output-run-start-stop-minimize-info">
<h2>Restart, fix_modify, output, run start/stop, minimize info<a class="headerlink" href="#restart-fix-modify-output-run-start-stop-minimize-info" title="Permalink to this headline">¶</a></h2>
<p>No information about this fix is written to <a class="reference internal" href="restart.html"><em>binary restart files</em></a>. None of the <a class="reference internal" href="fix_modify.html"><em>fix_modify</em></a> options
are relevant to this fix. No global or per-atom quantities are stored
by this fix for access by various <span class="xref std std-ref">output commands</span>. No parameter of this fix can be
used with the <em>start/stop</em> keywords of the <a class="reference internal" href="run.html"><em>run</em></a> command.
This fix is not invoked during <a class="reference internal" href="minimize.html"><em>energy minimization</em></a>.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
<p>Can only be used if a lattice-Boltzmann fluid has been created via the
<a class="reference internal" href="fix_lb_fluid.html"><em>fix lb/fluid</em></a> command, and must come after this
command.</p>
<p>This fix is part of the USER-LB package. It is only enabled if LAMMPS
was built with that package. See the <a class="reference internal" href="Section_start.html#start-3"><span>Making LAMMPS</span></a> section for more info.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
<p><a class="reference internal" href="fix_momentum.html"><em>fix momentum</em></a>, <a class="reference internal" href="fix_lb_fluid.html"><em>fix lb/fluid</em></a></p>
</div>
<div class="section" id="default">
<h2>Default<a class="headerlink" href="#default" title="Permalink to this headline">¶</a></h2>
<p>Zeros the total system linear momentum in each dimension.</p>
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