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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_accelerate.html">5. Accelerating LAMMPS performance</a></li>
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<div class="section" id="compute-bond-local-command">
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<span id="index-0"></span><h1>compute bond/local 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">bond</span><span class="o">/</span><span class="n">local</span> <span class="n">value1</span> <span class="n">value2</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="compute.html"><span class="doc">compute</span></a> command</li>
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<li>bond/local = style name of this compute command</li>
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<li>one or more values may be appended</li>
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<li>value = <em>dist</em> or <em>eng</em> or <em>force</em></li>
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</ul>
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<pre class="literal-block">
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<em>dist</em> = bond distance
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<em>eng</em> = bond energy
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<em>force</em> = bond force
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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">compute</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">bond</span><span class="o">/</span><span class="n">local</span> <span class="n">eng</span>
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<span class="n">compute</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">bond</span><span class="o">/</span><span class="n">local</span> <span class="n">dist</span> <span class="n">eng</span> <span class="n">force</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 properties of individual bond
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interactions. The number of datums generated, aggregated across all
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processors, equals the number of bonds in the system, modified
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by the group parameter as explained below.</p>
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<p>The value <em>dist</em> is the length of the bond.</p>
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<p>The value <em>eng</em> is the interaction energy for the bond.</p>
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<p>The value <em>force</em> is the force acting between the pair of atoms in the
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bond.</p>
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<p>The local data stored by this command is generated by looping over all
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the atoms owned on a processor and their bonds. A bond will only be
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included if both atoms in the bond are in the specified compute group.
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Any bonds that have been broken (see the <a class="reference internal" href="bond_style.html"><span class="doc">bond_style</span></a>
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command) by setting their bond type to 0 are not included. Bonds that
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have been turned off (see the <a class="reference internal" href="fix_shake.html"><span class="doc">fix shake</span></a> or
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<a class="reference internal" href="delete_bonds.html"><span class="doc">delete_bonds</span></a> commands) by setting their bond type
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negative are written into the file, but their energy will be 0.0.</p>
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<p>Note that as atoms migrate from processor to processor, there will be
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no consistent ordering of the entries within the local vector or array
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from one timestep to the next. The only consistency that is
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guaranteed is that the ordering on a particular timestep will be the
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same for local vectors or arrays generated by other compute commands.
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For example, bond output from the <a class="reference internal" href="compute_property_local.html"><span class="doc">compute property/local</span></a> command can be combined
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with data from this command and output by the <a class="reference internal" href="dump.html"><span class="doc">dump local</span></a>
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command in a consistent way.</p>
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<p>Here is an example of how to do this:</p>
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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="nb">all</span> <span class="nb">property</span><span class="o">/</span><span class="n">local</span> <span class="n">btype</span> <span class="n">batom1</span> <span class="n">batom2</span>
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<span class="n">compute</span> <span class="mi">2</span> <span class="nb">all</span> <span class="n">bond</span><span class="o">/</span><span class="n">local</span> <span class="n">dist</span> <span class="n">eng</span>
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<span class="n">dump</span> <span class="mi">1</span> <span class="nb">all</span> <span class="n">local</span> <span class="mi">1000</span> <span class="n">tmp</span><span class="o">.</span><span class="n">dump</span> <span class="n">index</span> <span class="n">c_1</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="n">c_1</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span> <span class="n">c_1</span><span class="p">[</span><span class="mi">3</span><span class="p">]</span> <span class="n">c_2</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="n">c_2</span><span class="p">[</span><span class="mi">2</span><span class="p">]</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 local vector or local array depending on the
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number of keywords. The length of the vector or number of rows in the
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array is the number of bonds. If a single keyword is specified, a
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local vector is produced. If two or more keywords are specified, a
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local array is produced where the number of columns = the number of
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keywords. The vector or array can be accessed by any command that
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uses local values from a compute as input. See <a class="reference internal" href="Section_howto.html#howto-15"><span class="std std-ref">this section</span></a> for an overview of LAMMPS output
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options.</p>
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<p>The output for <em>dist</em> will be in distance <a class="reference internal" href="units.html"><span class="doc">units</span></a>. The
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output for <em>eng</em> will be in energy <a class="reference internal" href="units.html"><span class="doc">units</span></a>. The output for
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<em>force</em> will be in force <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="dump.html"><span class="doc">dump local</span></a>, <a class="reference internal" href="compute_property_local.html"><span class="doc">compute property/local</span></a></p>
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<p><strong>Default:</strong> none</p>
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