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lammps/doc/compute_variable_atom.txt
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compute_variable_atom.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/atom command :h3
[Syntax:]
compute ID group-ID variable/atom 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 for each atom :ul
[Examples:]
compute 1 flow variable/atom myVar :pre
[Description:]
Define a computation that calculates a formula for each atom in the
group. The per-atom quantities can be output via the "dump
custom"_dump.html command or spatially averaged via the "fix
ave/spatial"_fix_ave_spatial.html command.
The formula is defined by the "variable atom"_variable.html command.
A variable of style {atom} 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 compute the xy kinectic energy of
atoms in the flow group and include the values in dumped snapshots of
the system.
variable xy atom mult(0.5,add(mult(vx\[\],vx\[\]),mult(vy\[\],vy\[\])))
compute ke flow variable/atom xy
dump 1 flow custom 1000 dump.flow tag type x y z c_ke :pre
If the dump line were replaced by
fix 1 flow ave/spatial 100 1000 z lower 2.0 ke.profile compute ke :pre
then the xy kinetic energy values would be averaged by z layer and the
layer averages written periodically to the file ke.profile.
[Restrictions:] none
[Related commands:]
"dump custom"_dump.html, "fix ave/spatial"_fix_ave_spatial.html
[Default:] none
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