git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@491 f3b2605a-c512-4ea7-a41b-209d697bcdaa

doc/compute_variable.txt

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+"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
+
+:link(lws,http://lammps.sandia.gov)
+:link(ld,Manual.html)
+:link(lc,Section_commands.html#comm)
+
+:line
+
+compute variable command :h3
+
+[Syntax:]
+
+compute ID group-ID variable name :pre
+
+ID, group-ID are documented in "compute"_compute.html command
+variable/atom = style name of this compute command
+name = variable name to invoke to compute a scalar quantity :ul
+
+[Examples:]
+
+compute 1 all variable myTemp :pre
+
+[Description:]
+
+Define a computation that calculates a formula that returns a scalar
+quantity.  This quantity can be time averaged and output via the "fix
+ave/time"_fix_ave_time.html command.  It could also be output via the
+"thermo_style custom"_thermo_style.html command, although it makes
+more sense to access the variable directly in this case.
+
+The formula is defined by the "variable equal"_variable.html command.
+A variable of style {equal} can access properties of the system, such
+as volume or temperature, and also reference individual atom
+attributes, such as its coordinates or velocity.
+
+For example, these 3 commands would time average the system density
+(assuming the volume fluctuates) temperature and output the average
+value periodically to the file den.profile:
+
+variable den equal div(atoms,vol)
+compute density all variable den
+fix 1 all ave/time 1 1000 density 0 den.profile :pre
+
+[Restrictions:] none
+
+[Related commands:]
+
+"fix ave/time"_fix_ave_time.html, "variable"_variable.html
+
+[Default:] none