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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_start.html">2. Getting Started</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_howto.html">6. How-to discussions</a></li>
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<li>compute omega/chunk command</li>
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<div class="section" id="compute-omega-chunk-command">
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<span id="index-0"></span><h1>compute omega/chunk 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">compute</span> <span class="n">ID</span> <span class="n">group</span><span class="o">-</span><span class="n">ID</span> <span class="n">omega</span><span class="o">/</span><span class="n">chunk</span> <span class="n">chunkID</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="compute.html"><span class="doc">compute</span></a> command</li>
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<li>omega/chunk = style name of this compute command</li>
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<li>chunkID = ID of <a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom</span></a> command</li>
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</ul>
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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">compute</span> <span class="mi">1</span> <span class="n">fluid</span> <span class="n">omega</span><span class="o">/</span><span class="n">chunk</span> <span class="n">molchunk</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>Define a computation that calculates the angular velocity (omega) of
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multiple chunks of atoms.</p>
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<p>In LAMMPS, chunks are collections of atoms defined by a <a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom</span></a> command, which assigns each atom
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to a single chunk (or no chunk). The ID for this command is specified
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as chunkID. For example, a single chunk could be the atoms in a
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molecule or atoms in a spatial bin. See the <a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom</span></a> doc page and “<a class="reference internal" href="Section_howto.html#howto-23"><span class="std std-ref">Section_howto 23</span></a> for details of how chunks can be
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defined and examples of how they can be used to measure properties of
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a system.</p>
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<p>This compute calculates the 3 components of the angular velocity
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vector for each chunk, via the formula L = Iw where L is the angular
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momentum vector of the chunk, I is its moment of inertia tensor, and w
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is omega = angular velocity of the chunk. The calculation includes
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all effects due to atoms passing thru periodic boundaries.</p>
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<p>Note that only atoms in the specified group contribute to the
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calculation. The <a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom</span></a> command
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defines its own group; atoms will have a chunk ID = 0 if they are not
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in that group, signifying they are not assigned to a chunk, and will
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thus also not contribute to this calculation. You can specify the
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“all” group for this command if you simply want to include atoms with
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non-zero chunk IDs.</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">The coordinates of an atom contribute to the chunk’s angular
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velocity in “unwrapped” form, by using the image flags associated with
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each atom. See the <a class="reference internal" href="dump.html"><span class="doc">dump custom</span></a> command for a discussion
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of “unwrapped” coordinates. See the Atoms section of the
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<a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a> command for a discussion of image flags and
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how they are set for each atom. You can reset the image flags
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(e.g. to 0) before invoking this compute by using the <a class="reference internal" href="set.html"><span class="doc">set image</span></a> command.</p>
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</div>
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<p>The simplest way to output the results of the compute omega/chunk
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calculation to a file is to use the <a class="reference internal" href="fix_ave_time.html"><span class="doc">fix ave/time</span></a>
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command, for example:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">compute</span> <span class="n">cc1</span> <span class="nb">all</span> <span class="n">chunk</span><span class="o">/</span><span class="n">atom</span> <span class="n">molecule</span>
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<span class="n">compute</span> <span class="n">myChunk</span> <span class="nb">all</span> <span class="n">omega</span><span class="o">/</span><span class="n">chunk</span> <span class="n">cc1</span>
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<span class="n">fix</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">ave</span><span class="o">/</span><span class="n">time</span> <span class="mi">100</span> <span class="mi">1</span> <span class="mi">100</span> <span class="n">c_myChunk</span> <span class="n">file</span> <span class="n">tmp</span><span class="o">.</span><span class="n">out</span> <span class="n">mode</span> <span class="n">vector</span>
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</pre></div>
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</div>
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<p><strong>Output info:</strong></p>
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<p>This compute calculates a global array where the number of rows = the
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number of chunks <em>Nchunk</em> as calculated by the specified <a class="reference internal" href="compute_chunk_atom.html"><span class="doc">compute chunk/atom</span></a> command. The number of columns =
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3 for the 3 xyz components of the angular velocity for each chunk.
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These values can be accessed by any command that uses global array
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values from a compute as input. See <a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">Section_howto 15</span></a> for an overview of LAMMPS output
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options.</p>
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<p>The array values are “intensive”. The array values will be in
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velocity/distance <a class="reference internal" href="units.html"><span class="doc">units</span></a>.</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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<blockquote>
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<div>none</div></blockquote>
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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="variable.html"><span class="doc">variable omega() function</span></a></p>
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<p><strong>Default:</strong> none</p>
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