forked from lijiext/lammps
62 lines
1.9 KiB
HTML
62 lines
1.9 KiB
HTML
<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 variable/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 variable/atom name
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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>variable/atom = style name of this compute command
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<LI>name = variable name to invoke for each atom
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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 flow variable/atom myVar
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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 a formula for each atom in the
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group. The per-atom quantities can be output via the <A HREF = "dump.html">dump
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custom</A> command or spatially averaged via the <A HREF = "fix_ave_spatial.html">fix
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ave/spatial</A> command.
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</P>
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<P>The formula is defined by the <A HREF = "variable.html">variable atom</A> command.
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A variable of style <I>atom</I> can access properties of the system, such
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as volume or temperature, and also reference individual atom
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attributes, such as its coordinates or velocity.
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</P>
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<P>For example, these 3 commands would compute the xy kinectic energy of
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atoms in the flow group and include the values in dumped snapshots of
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the system.
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</P>
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<PRE>variable xy atom mult(0.5,add(mult(vx[],vx[]),mult(vy[],vy[])))
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compute ke flow variable/atom xy
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dump 1 flow custom 1000 dump.flow tag type x y z c_ke
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</PRE>
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<P>If the dump line were replaced by
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</P>
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<PRE>fix 1 flow ave/spatial 100 1000 z lower 2.0 ke.profile compute ke
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</PRE>
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<P>then the xy kinetic energy values would be averaged by z layer and the
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layer averages written periodically to the file ke.profile.
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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 = "dump.html">dump custom</A>, <A HREF = "fix_ave_spatial.html">fix ave/spatial</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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