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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>
</CENTER>
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<H3>compute dilatation/atom command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>compute ID group-ID dilatation/atom
</PRE>
<UL><LI>ID, group-ID are documented in compute command
<LI>dilation/atom = style name of this compute command
</UL>
<P><B>Examples:</B>
</P>
<PRE>compute 1 all dilatation/atom
</PRE>
<P><B>Description:</B>
</P>
<P>Define a computation that calculates the per-atom dilatation for each
atom in a group. This is a quantity relevant for <A HREF = "pair_peri.html">Peridynamics
models</A>. See <A HREF = "PDF/PDLammps_overview.pdf">this document</A>
for an overview of LAMMPS commands for Peridynamics modeling.
</P>
<P>For small deformation, dilatation of is the measure of the volumetric
strain.
</P>
<P>The dilatation "theta" for each peridynamic particle I is calculated
as a sum over its neighbors with unbroken bonds, where the
contribution of the IJ pair is a function of the change in bond length
(versus the initial length in the reference state), the volume
fraction of the particles and an influence function. See the
<A HREF = "http://www.sandia.gov/~mlparks/papers/PDLAMMPS.pdf">PDLAMMPS user
guide</A> for a formal
definition of dilatation.
</P>
<P>This command can only be used with a subset of the Peridynamic <A HREF = "pair_peri.html">pair
styles</A>: peri/lps, peri/ves and peri/eps.
</P>
<P>The dilatation value will be 0.0 for atoms not in the specified
compute group.
</P>
<P><B>Output info:</B>
</P>
<P>This compute calculates a per-atom vector, which can be accessed by
any command that uses per-atom values from a compute as input. See
Section_howto 15 for an overview of LAMMPS output options.
</P>
<P>The per-atom vector values are unitlesss numbers (theta) >= 0.0.
</P>
<P><B>Restrictions:</B>
</P>
<P>This compute is part of the PERI package. It is only enabled if
LAMMPS was built with that package. See the <A HREF = "Section_start.html#start_3">Making
LAMMPS</A> section for more info.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "compute_damage.html">compute damage</A>, <A HREF = "compute_plasticity.html">compute
plasticity</A>
</P>
<P><B>Default:</B> none
</P>
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