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<title>compute property/local command &mdash; LAMMPS 9 Dec 2015 documentation</title>
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<div class="section" id="compute-property-local-command">
<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>
<div class="section" id="syntax">
<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline"></a></h2>
<div class="highlight-python"><div class="highlight"><pre>compute ID group-ID property/local input1 input2 ...
</pre></div>
</div>
<ul class="simple">
<li>ID, group-ID are documented in <a class="reference internal" href="compute.html"><em>compute</em></a> command</li>
<li>property/local = style name of this compute command</li>
<li>input = one or more attributes</li>
</ul>
<div class="highlight-python"><div class="highlight"><pre>possible attributes = natom1 natom2 ntype1 ntype2
patom1 patom2 ptype1 ptype2
batom1 batom2 btype
aatom1 aatom2 aatom3 atype
datom1 datom2 datom3 dtype
iatom1 iatom2 iatom3 itype
</pre></div>
</div>
<div class="highlight-python"><div class="highlight"><pre>natom1, natom2 = IDs of 2 atoms in each pair (within neighbor cutoff)
ntype1, ntype2 = type of 2 atoms in each pair (within neighbor cutoff)
patom1, patom2 = IDs of 2 atoms in each pair (within force cutoff)
ptype1, ptype2 = type of 2 atoms in each pair (within force cutoff)
batom1, batom2 = IDs of 2 atoms in each bond
btype = bond type of each bond
aatom1, aatom2, aatom3 = IDs of 3 atoms in each angle
atype = angle type of each angle
datom1, datom2, datom3, datom4 = IDs of 4 atoms in each dihedral
dtype = dihedral type of each dihedral
iatom1, iatom2, iatom3, iatom4 = IDs of 4 atoms in each improper
itype = improper type of each improper
</pre></div>
</div>
</div>
<div class="section" id="examples">
<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline"></a></h2>
<div class="highlight-python"><div class="highlight"><pre>compute 1 all property/local btype batom1 batom2
compute 1 all property/local atype aatom2
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline"></a></h2>
<p>Define a computation that stores the specified attributes as local
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
to bond information, then the number of datums generated, aggregated
across all processors, equals the number of bonds in the system.
Ditto for pairs, angles, etc.</p>
<p>If multiple input attributes are specified then they must all generate
the same amount of information, so that the resulting local array has
the same number of rows for each column. This means that only bond
attributes can be specified together, or angle attributes, etc. Bond
and angle attributes can not be mixed in the same compute
property/local command.</p>
<p>If the inputs are pair attributes, the local data is generated by
looping over the pairwise neighbor list. Info about an individual
pairwise interaction will only be included if both atoms in the pair
are in the specified compute group. For <em>natom1</em> and <em>natom2</em>, all
atom pairs in the neighbor list are considered (out to the neighbor
cutoff = force cutoff + <a class="reference internal" href="neighbor.html"><em>neighbor skin</em></a>). For <em>patom1</em>
and <em>patom2</em>, the distance between the atoms must be less than the
force cutoff distance for that pair to be included, as defined by the
<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>
commands.</p>
<p>If the inputs are bond, angle, etc attributes, the local data is
generated by looping over all the atoms owned on a processor and
extracting bond, angle, etc info. For bonds, info about an individual
bond will only be included if both atoms in the bond are in the
specified compute group. Likewise for angles, dihedrals, etc.</p>
<p>For bonds and angles, a bonds/angles that have been broken by setting
their bond/angle type to 0 will not be included. Bonds/angles that
have been turned off (see the <a class="reference internal" href="fix_shake.html"><em>fix shake</em></a> or
<a class="reference internal" href="delete_bonds.html"><em>delete_bonds</em></a> commands) by setting their bond/angle
type negative are written into the file. This is consistent with the
<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>
<p>Note that as atoms migrate from processor to processor, there will be
no consistent ordering of the entries within the local vector or array
from one timestep to the next. The only consistency that is
guaranteed is that the ordering on a particular timestep will be the
same for local vectors or arrays generated by other compute commands.
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
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>
<p>The <em>natom1</em> and <em>natom2</em>, or <em>patom1</em> and <em>patom2</em> attributes refer
to the atom IDs of the 2 atoms in each pairwise interaction computed
by the <a class="reference internal" href="pair_style.html"><em>pair_style</em></a> command. The <em>ntype1</em> and
<em>ntype2</em>, or <em>ptype1</em> and <em>ptype2</em> attributes refer to the atom types
of the 2 atoms in each pairwise interaction.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">For pairs, if two atoms I,J are involved in 1-2, 1-3, 1-4
interactions within the molecular topology, their pairwise interaction
may be turned off, and thus they may not appear in the neighbor list,
and will not be part of the local data created by this command. More
specifically, this may be true of I,J pairs with a weighting factor of
0.0; pairs with a non-zero weighting factor are included. The
weighting factors for 1-2, 1-3, and 1-4 pairwise interactions are set
by the <a class="reference internal" href="special_bonds.html"><em>special_bonds</em></a> command.</p>
</div>
<p>The <em>batom1</em> and <em>batom2</em> attributes refer to the atom IDs of the 2
atoms in each <a class="reference internal" href="bond_style.html"><em>bond</em></a>. The <em>btype</em> attribute refers to
the type of the bond, from 1 to Nbtypes = # of bond types. The number
of bond types is defined in the data file read by the
<a class="reference internal" href="read_data.html"><em>read_data</em></a> command.</p>
<p>The attributes that start with &#8220;a&#8221;, &#8220;d&#8221;, &#8220;i&#8221;, refer to similar values
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
<a class="reference internal" href="improper_style.html"><em>impropers</em></a>.</p>
<p><strong>Output info:</strong></p>
<p>This compute calculates a local vector or local array depending on the
number of input values. The length of the vector or number of rows in
the array is the number of bonds, angles, etc. If a single input is
specified, a local vector is produced. If two or more inputs are
specified, a local array is produced where the number of columns = the
number of inputs. The vector or array can be accessed by any command
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
options.</p>
<p>The vector or array values will be integers that correspond to the
specified attribute.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline"></a></h2>
<blockquote>
<div>none</div></blockquote>
</div>
<div class="section" id="related-commands">
<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline"></a></h2>
<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>
<p><strong>Default:</strong> none</p>
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