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<div class="section" id="fix-oneway-command">
<span id="index-0"></span><h1>fix oneway command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">fix</span> <span class="n">ID</span> <span class="n">group</span><span class="o">-</span><span class="n">ID</span> <span class="n">oneway</span> <span class="n">N</span> <span class="n">region</span><span class="o">-</span><span class="n">ID</span> <span class="n">direction</span>
</pre></div>
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<ul class="simple">
<li>ID, group-ID are documented in <a class="reference internal" href="fix.html"><span class="doc">fix</span></a> command</li>
<li>oneway = style name of this fix command</li>
<li>N = apply this fix every this many timesteps</li>
<li>region-ID = ID of region where fix is active</li>
<li>direction = <em>x</em> or <em>-x</em> or <em>y</em> or <em>-y</em> or <em>z</em> or <em>-z</em> = coordinate and direction of the oneway constraint</li>
</ul>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">fix</span> <span class="n">ions</span> <span class="n">oneway</span> <span class="mi">10</span> <span class="n">semi</span> <span class="o">-</span><span class="n">x</span>
<span class="n">fix</span> <span class="nb">all</span> <span class="n">oneway</span> <span class="mi">1</span> <span class="n">left</span> <span class="o">-</span><span class="n">z</span>
<span class="n">fix</span> <span class="nb">all</span> <span class="n">oneway</span> <span class="mi">1</span> <span class="n">right</span> <span class="n">z</span>
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>Enforce that particles in the group and in a given region can only
move in one direction. This is done by reversing a particle&#8217;s
velocity component, if it has the wrong sign in the specified
dimension. The effect is that the particle moves in one direction
only.</p>
<p>This can be used, for example, as a simple model of a semi-permeable
membrane, or as an implementation of Maxwell&#8217;s demon.</p>
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<h2>Restart, fix_modify, output, run start/stop, minimize info</h2>
<p>No information about this fix is written to <a class="reference internal" href="restart.html"><span class="doc">binary restart files</span></a>. None of the <a class="reference internal" href="fix_modify.html"><span class="doc">fix_modify</span></a> options
are relevant to this fix. No global or per-atom quantities are stored
by this fix for access by various <a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">output commands</span></a>. No parameter of this fix can
be used with the <em>start/stop</em> keywords of the <a class="reference internal" href="run.html"><span class="doc">run</span></a> command.
This fix is not invoked during <a class="reference internal" href="minimize.html"><span class="doc">energy minimization</span></a>.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<blockquote>
<div>none</div></blockquote>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="fix_wall_reflect.html"><span class="doc">fix wall/reflect</span></a> command</p>
<p><strong>Default:</strong> none</p>
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