forked from lijiext/lammps
56 lines
1.7 KiB
HTML
56 lines
1.7 KiB
HTML
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<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 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 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 to compute a scalar quantity
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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 variable myTemp
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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 that returns a scalar
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quantity. This quantity can be time averaged and output via the <A HREF = "fix_ave_time.html">fix
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ave/time</A> command. It could also be output via the
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<A HREF = "thermo_style.html">thermo_style custom</A> command, although it makes
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more sense to access the variable directly in this case.
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</P>
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<P>The formula is defined by the <A HREF = "variable.html">variable equal</A> command.
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A variable of style <I>equal</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 time average the system density
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(assuming the volume fluctuates) temperature and output the average
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value periodically to the file den.profile:
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</P>
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<PRE>variable den equal div(atoms,vol)
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compute density all variable den
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fix 1 all ave/time 1 1000 density 0 den.profile
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</PRE>
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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_time.html">fix ave/time</A>, <A HREF = "variable.html">variable</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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