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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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<H3>compute attribute/atom command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>compute ID group-ID attribute/atom style
</PRE>
<UL><LI>ID, group-ID are documented in <A HREF = "compute.html">compute</A> command
<LI>attribute/atom = style name of this compute command
<LI>style = <I>x</I> or <I>y</I> or <I>z</I> or <I>xu</I> or <I>yu</I> or <I>zu</I> or <I>vx</I> or <I>vy</I> or <I>vz</I> or <I>fx</I> or <I>fy</I> or <I>fz</I> or <I>xyz</I> or <I>v</I> or <I>f</I>
</UL>
<P><B>Examples:</B>
</P>
<PRE>compute 1 all attribute/atom vy
compute mine all attribute/atom xyz
</PRE>
<P><B>Description:</B>
</P>
<P>Define a computation that calculates (or simply stores) one or more
attributes for each atom in a group. This is useful for input to the
<A HREF = "fix_ave_spatial.html">fix ave/spatial</A> command to do spatial averaging
by layers or to the <A HREF = "fix_ave_atom.html">fix ave/atom</A> command to
perform time-averaging of per-atom quantities. The attribute values
can also be output directly by the <A HREF = "dump.html">dump custom</A> command,
but it has keywords that output these quantities without the need to
define an additional compute.
</P>
<P>The value of the attribute will be 0.0 for atoms not in the specified
compute group.
</P>
<P>The styles <I>x</I>, <I>y</I>, <I>z</I>, <I>xu</I>, <I>yu</I>, <I>zu</I>, <I>vx</I>, <I>vy</I>, <I>vz</I>, <I>fx</I>,
<I>fy</I>, and <I>fz</I> each store a single scalar value per atom.
</P>
<P>The <I>x</I>, <I>y</I>, <I>z</I> keywords store atom coordinate in the appropriate
distance <A HREF = "units.html">units</A> (Angstroms, sigma, etc) and will always be
inside (or slightly outside) the simulation box. Use <I>xu</I>, <I>yu</I>, <I>zu</I>
if you want the coordinates "unwrapped" by the image flags for each
atom. Unwrapped means that if the atom has passed thru a periodic
boundary one or more times, the value is printed for what the
coordinate would be if it had not been wrapped back into the periodic
box. Note that using <I>xu</I>, <I>yu</I>, <I>zu</I> means that the coordinate
values may be far outside the simulation box.
</P>
<P>Note that if you want to compute the time-averaged position of an atom
coordinate that could pass thru a periodic boundary (e.g. via the <A HREF = "fix_ave_atom.html">fix
ave/atom</A> command), you probably want to use <I>xu</I>
instead of <I>x</I>.
</P>
<P>The styles <I>xyz</I>, <I>v</I>, and <I>f</I> each store a vector of 3 quantities per
atom.
</P>
<P>Note that the various commands that reference this compute use a
different syntax for accessing scalar versus vector values, e.g. c_ID
versus c_ID[2].
</P>
<P><B>Restrictions:</B> none
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "fix_ave_atom.html">fix ave/atom</A>, <A HREF = "fix_ave_spatial.html">fix
ave/spatial</A>, <A HREF = "dump.html">dump custom</A>
</P>
<P><B>Default:</B> none
</P>
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