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<title>compute property/local command — LAMMPS 15 May 2015 version documentation</title>
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<div class="section" id="compute-property-local-command">
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<span id="index-0"></span><h1>compute property/local command<a class="headerlink" href="#compute-property-local-command" title="Permalink to this headline">¶</a></h1>
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<div class="section" id="syntax">
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<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>compute ID group-ID property/local input1 input2 ...
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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"><em>compute</em></a> command</li>
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<li>property/local = style name of this compute command</li>
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<li>input = one or more attributes</li>
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</ul>
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<div class="highlight-python"><div class="highlight"><pre>possible attributes = natom1 natom2 ntype1 ntype2
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patom1 patom2 ptype1 ptype2
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batom1 batom2 btype
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aatom1 aatom2 aatom3 atype
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datom1 datom2 datom3 dtype
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iatom1 iatom2 iatom3 itype
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</pre></div>
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</div>
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<div class="highlight-python"><div class="highlight"><pre>natom1, natom2 = IDs of 2 atoms in each pair (within neighbor cutoff)
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ntype1, ntype2 = type of 2 atoms in each pair (within neighbor cutoff)
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patom1, patom2 = IDs of 2 atoms in each pair (within force cutoff)
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ptype1, ptype2 = type of 2 atoms in each pair (within force cutoff)
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batom1, batom2 = IDs of 2 atoms in each bond
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btype = bond type of each bond
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aatom1, aatom2, aatom3 = IDs of 3 atoms in each angle
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atype = angle type of each angle
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datom1, datom2, datom3, datom4 = IDs of 4 atoms in each dihedral
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dtype = dihedral type of each dihedral
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iatom1, iatom2, iatom3, iatom4 = IDs of 4 atoms in each improper
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itype = improper type of each improper
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</pre></div>
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</div>
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</div>
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<div class="section" id="examples">
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<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>compute 1 all property/local btype batom1 batom2
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compute 1 all property/local atype aatom2
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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<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
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<p>Define a computation that stores the specified attributes as local
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data so it can be accessed by other <a class="reference internal" href="Section_howto.html#howto-15"><span>output commands</span></a>. If the input attributes refer
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to bond information, then the number of datums generated, aggregated
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across all processors, equals the number of bonds in the system.
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Ditto for pairs, angles, etc.</p>
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<p>If multiple input attributes are specified then they must all generate
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the same amount of information, so that the resulting local array has
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the same number of rows for each column. This means that only bond
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attributes can be specified together, or angle attributes, etc. Bond
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and angle attributes can not be mixed in the same compute
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property/local command.</p>
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<p>If the inputs are pair attributes, the local data is generated by
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looping over the pairwise neighbor list. Info about an individual
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pairwise interaction will only be included if both atoms in the pair
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are in the specified compute group. For <em>natom1</em> and <em>natom2</em>, all
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atom pairs in the neighbor list are considered (out to the neighbor
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cutoff = force cutoff + <a class="reference internal" href="neighbor.html"><em>neighbor skin</em></a>). For <em>patom1</em>
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and <em>patom2</em>, the distance between the atoms must be less than the
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force cutoff distance for that pair to be included, as defined by the
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<a class="reference internal" href="pair_style.html"><em>pair_style</em></a> and <a class="reference internal" href="pair_coeff.html"><em>pair_coeff</em></a>
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commands.</p>
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<p>If the inputs are bond, angle, etc attributes, the local data is
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generated by looping over all the atoms owned on a processor and
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extracting bond, angle, etc info. For bonds, info about an individual
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bond will only be included if both atoms in the bond are in the
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specified compute group. Likewise for angles, dihedrals, etc.</p>
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<p>For bonds and angles, a bonds/angles that have been broken by setting
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their bond/angle type to 0 will not be included. Bonds/angles that
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have been turned off (see the <a class="reference internal" href="fix_shake.html"><em>fix shake</em></a> or
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<a class="reference internal" href="delete_bonds.html"><em>delete_bonds</em></a> commands) by setting their bond/angle
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type negative are written into the file. This is consistent with the
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<a class="reference internal" href="compute_bond_local.html"><em>compute bond/local</em></a> and <a class="reference internal" href="compute_angle_local.html"><em>compute angle/local</em></a> commands</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, output from the <a class="reference internal" href="compute_bond_local.html"><em>compute bond/local</em></a> command can be combined with bond
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atom indices from this command and output by the <a class="reference internal" href="dump.html"><em>dump local</em></a> command in a consistent way.</p>
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<p>The <em>natom1</em> and <em>natom2</em>, or <em>patom1</em> and <em>patom2</em> attributes refer
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to the atom IDs of the 2 atoms in each pairwise interaction computed
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by the <a class="reference internal" href="pair_style.html"><em>pair_style</em></a> command. The <em>ntype1</em> and
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<em>ntype2</em>, or <em>ptype1</em> and <em>ptype2</em> attributes refer to the atom types
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of the 2 atoms in each pairwise interaction.</p>
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<div class="admonition warning">
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<p class="first admonition-title">Warning</p>
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<p class="last">For pairs, if two atoms I,J are involved in 1-2, 1-3,
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1-4 interactions within the molecular topology, their pairwise
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interaction may be turned off, and thus they may not appear in the
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neighbor list, and will not be part of the local data created by this
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command. More specifically, this may be true of I,J pairs with a
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weighting factor of 0.0; pairs with a non-zero weighting factor are
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included. The weighting factors for 1-2, 1-3, and 1-4 pairwise
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interactions are set by the <a class="reference internal" href="special_bonds.html"><em>special_bonds</em></a>
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command.</p>
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</div>
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<p>The <em>batom1</em> and <em>batom2</em> attributes refer to the atom IDs of the 2
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atoms in each <a class="reference internal" href="bond_style.html"><em>bond</em></a>. The <em>btype</em> attribute refers to
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the type of the bond, from 1 to Nbtypes = # of bond types. The number
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of bond types is defined in the data file read by the
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<a class="reference internal" href="read_data.html"><em>read_data</em></a> command.</p>
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<p>The attributes that start with “a”, “d”, “i”, refer to similar values
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for <a class="reference internal" href="angle_style.html"><em>angles</em></a>, <a class="reference internal" href="dihedral_style.html"><em>dihedrals</em></a>, and
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<a class="reference internal" href="improper_style.html"><em>impropers</em></a>.</p>
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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 input values. The length of the vector or number of rows in
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the array is the number of bonds, angles, etc. If a single input is
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specified, a local vector is produced. If two or more inputs are
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specified, a local array is produced where the number of columns = the
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number of inputs. The vector or array can be accessed by any command
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that uses local values from a compute as input. See <a class="reference internal" href="Section_howto.html#howto-15"><span>this section</span></a> for an overview of LAMMPS output
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options.</p>
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<p>The vector or array values will be integers that correspond to the
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specified attribute.</p>
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</div>
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<div class="section" id="restrictions">
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<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></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<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
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<p><a class="reference internal" href="dump.html"><em>dump local</em></a>, <a class="reference internal" href="compute_reduce.html"><em>compute reduce</em></a></p>
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<p><strong>Default:</strong> none</p>
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