2009-12-18 01:28:50 +08:00
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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
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<HR>
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<H3>compute property/local command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>compute ID group-ID property/local input1 input2 ...
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "compute.html">compute</A> command
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<LI>property/local = style name of this compute command
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<LI>input = one or more attributes
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2010-06-19 02:58:59 +08:00
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<PRE> possible attributes = natom1 natom2
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patom1 patom2
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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>
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2010-06-19 02:58:59 +08:00
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<PRE> natom1, natom2 = IDs 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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2009-12-22 07:01:36 +08:00
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batom1, batom2 = IDs of 2 atoms in each bond
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2009-12-18 01:28:50 +08:00
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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>
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</UL>
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<P><B>Examples:</B>
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</P>
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<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>
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<P><B>Description:</B>
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</P>
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2009-12-19 02:41:14 +08:00
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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 HREF = "Section_howto.html#howto_15">output
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commands</A>. If the input attributes refer
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to bond information, then the number of datums generated, aggregated
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2009-12-19 02:41:14 +08:00
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across all processors, equals the number of bonds in the system.
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Ditto for pairs, angles, etc.
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2009-12-18 01:28:50 +08:00
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</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.
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</P>
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2009-12-22 08:22:16 +08:00
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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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2010-06-19 02:58:59 +08:00
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are in the specified compute group. For <I>natom1</I> and <I>natom2</I>, 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 HREF = "neighbor.html">neighbor skin</A>). For <I>patom1</I>
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and <I>patom2</I>, 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 HREF = "pair_style.html">pair_style</A> and <A HREF = "pair_coeff.html">pair_coeff</A>
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commands.
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2009-12-18 01:28:50 +08:00
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</P>
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2009-12-22 08:22:16 +08:00
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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.
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2009-12-22 07:01:36 +08:00
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</P>
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2009-12-22 08:22:16 +08:00
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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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2009-12-18 01:28:50 +08:00
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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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2009-12-19 02:41:14 +08:00
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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 HREF = "compute_bond_local.html">compute
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bond/local</A> command can be combined with bond
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atom indices from this command and output by the <A HREF = "dump.html">dump
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local</A> command in a consistent way.
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2009-12-18 01:28:50 +08:00
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</P>
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2010-06-19 02:58:59 +08:00
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<P>The <I>natom1</I> and <I>natom2</I>, or <I>patom1</I> and <I>patom2</I> 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 HREF = "pair_style.html">pair_style</A> command.
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2009-12-22 07:56:43 +08:00
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</P>
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<P>IMPORTANT NOTE: 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 HREF = "special_bonds.html">special_bonds</A>
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command.
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</P>
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2009-12-22 07:01:36 +08:00
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<P>The <I>batom1</I> and <I>batom2</I> attributes refer to the atom IDs of the 2
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atoms in each <A HREF = "bond_style.html">bond</A>. The <I>btype</I> 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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2009-12-18 01:28:50 +08:00
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<A HREF = "read_data.html">read_data</A> command. The attributes that start with
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"a", "d", "i", refer to similar values for <A HREF = "angle_style.html">angles</A>,
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<A HREF = "dihedral_style.html">dihedrals</A>, and <A HREF = "improper_style.html">impropers</A>.
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</P>
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<P><B>Output info:</B>
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</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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2011-08-26 01:01:01 +08:00
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that uses local values from a compute as input. See <A HREF = "Section_howto.html#howto_15">this
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section</A> for an overview of LAMMPS output
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options.
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</P>
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2010-01-24 07:20:05 +08:00
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<P>The vector or array values will be integers that correspond to the
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specified attribute.
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</P>
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2009-12-18 01:28:50 +08:00
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<P><B>Restrictions:</B> none
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "dump.html">dump local</A>, <A HREF = "compute_reduce.html">compute reduce</A>
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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