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<div class="section" id="fix-smd-setvel-command">
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<span id="index-0"></span><h1>fix smd/setvel 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">fix</span> <span class="n">ID</span> <span class="n">group</span><span class="o">-</span><span class="n">ID</span> <span class="n">smd</span><span class="o">/</span><span class="n">setvel</span> <span class="n">vx</span> <span class="n">vy</span> <span class="n">vz</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>ID, group-ID are documented in <a class="reference internal" href="fix.html"><span class="doc">fix</span></a> command</li>
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<li>smd/setvel = style name of this fix command</li>
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<li>vx,vy,vz = velocity component values</li>
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<li>any of vx,vy,vz can be a variable (see below)</li>
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<li>zero or more keyword/value pairs may be appended to args</li>
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<li>keyword = <em>region</em></li>
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</ul>
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<pre class="literal-block">
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<em>region</em> value = region-ID
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region-ID = ID of region particles must be in to have their velocities set
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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">fix</span> <span class="n">top_velocity</span> <span class="n">top_group</span> <span class="n">setvel</span> <span class="mf">1.0</span> <span class="mf">0.0</span> <span class="mf">0.0</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>Set each component of velocity on each particle in the group to the specified
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values vx,vy,vz, regardless of the forces acting on the particle. This command can
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be used to impose velocity boundary conditions.</p>
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<p>Any of the vx,vy,vz values can be specified as NULL which means do not
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alter the velocity component in that dimension.</p>
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<p>This fix is indented to be used together with a time integration fix.</p>
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<p>Any of the 3 quantities defining the velocity components can be specified
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as an equal-style or atom-style <a class="reference internal" href="variable.html"><span class="doc">variable</span></a>, namely <em>vx</em>,
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<em>vy</em>, <em>vz</em>. If the value is a variable, it should be specified as
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v_name, where name is the variable name. In this case, the variable
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will be evaluated each timestep, and its value used to determine the
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force component.</p>
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<p>Equal-style variables can specify formulas with various mathematical
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functions, and include <a class="reference internal" href="thermo_style.html"><span class="doc">thermo_style</span></a> command
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keywords for the simulation box parameters and timestep and elapsed
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time. Thus it is easy to specify a time-dependent velocity field.</p>
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<p>Atom-style variables can specify the same formulas as equal-style
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variables but can also include per-atom values, such as atom
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coordinates. Thus it is easy to specify a spatially-dependent velocity
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field with optional time-dependence as well.</p>
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<p>If the <em>region</em> keyword is used, the particle must also be in the
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specified geometric <a class="reference internal" href="region.html"><span class="doc">region</span></a> in order to have its velocity set by this command.</p>
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</div>
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<hr class="docutils" />
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<div class="section" id="restart-fix-modify-output-run-start-stop-minimize-info">
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<h2>Restart, fix_modify, output, run start/stop, minimize info</h2>
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<p>Currently, no part of USER-SMD supports restarting nor minimization
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None of the <a class="reference internal" href="fix_modify.html"><span class="doc">fix_modify</span></a> options
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are relevant to this fix.</p>
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<p>This fix computes a global 3-vector of forces, which can be accessed
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by various <a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">output commands</span></a>. This is the
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total force on the group of atoms. The vector values calculated by this
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fix are “extensive”.</p>
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<p>No parameter of this fix can be used with the <em>start/stop</em> keywords of
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the <a class="reference internal" href="run.html"><span class="doc">run</span></a> command.</p>
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</div>
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<div class="section" id="restrictions">
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<h2>Restrictions</h2>
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<p>This fix is part of the USER-SMD package. It is only enabled if
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LAMMPS was built with that package. See the <a class="reference internal" href="Section_start.html#start-3"><span class="std std-ref">Making LAMMPS</span></a>
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section for more info.</p>
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<p><strong>Related commands:</strong> none</p>
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<p><strong>Default:</strong> none</p>
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