forked from lijiext/lammps
73 lines
2.9 KiB
HTML
73 lines
2.9 KiB
HTML
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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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</CENTER>
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<HR>
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<H3>compute attribute/atom 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 attribute/atom style
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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>attribute/atom = style name of this compute command
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<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>
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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 attribute/atom vy
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compute mine all attribute/atom xyz
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Define a computation that calculates (or simply stores) one or more
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attributes for each atom in a group. This is useful for input to the
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<A HREF = "fix_ave_spatial.html">fix ave/spatial</A> command to do spatial averaging
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by layers or to the <A HREF = "fix_ave_atom.html">fix ave/atom</A> command to
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perform time-averaging of per-atom quantities. The attribute values
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can also be output directly by the <A HREF = "dump.html">dump custom</A> command,
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but it has keywords that output these quantities without the need to
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define an additional compute.
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</P>
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<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>,
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<I>fy</I>, and <I>fz</I> each store a single scalar value per atom.
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</P>
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<P>The <I>x</I>, <I>y</I>, <I>z</I> keywords store atom coordinate in the appropriate
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distance <A HREF = "units.html">units</A> (Angstroms, sigma, etc) and will always be
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inside (or slightly outside) the simulation box. Use <I>xu</I>, <I>yu</I>, <I>zu</I>
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if you want the coordinates "unwrapped" by the image flags for each
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atom. Unwrapped means that if the atom has passed thru a periodic
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boundary one or more times, the value is printed for what the
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coordinate would be if it had not been wrapped back into the periodic
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box. Note that using <I>xu</I>, <I>yu</I>, <I>zu</I> means that the coordinate
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values may be far outside the simulation box.
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</P>
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<P>Note that if you want to compute the time-averaged position of an atom
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coordinate that could pass thru a periodic boundary (e.g. via the <A HREF = "fix_ave_atom.html">fix
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ave/atom</A> command), you probably want to use <I>xu</I>
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instead of <I>x</I>.
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</P>
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<P>The styles <I>xyz</I>, <I>v</I>, and <I>f</I> each store a vector of 3 quantities per
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atom.
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</P>
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<P>Note that the various commands that reference this compute use a
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different syntax for accessing scalar versus vector values, e.g. c_ID
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versus c_ID<B>2</B>.
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</P>
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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 = "fix_ave_atom.html">fix ave/atom</A>, <A HREF = "fix_ave_spatial.html">fix
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ave/spatial</A>, <A HREF = "dump.html">dump custom</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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