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### compute variable/atom command

Syntax:

    compute ID group-ID variable/atom name

- ID, group-ID are documented in compute command
- variable/atom = style name of this compute command
- name = variable name to invoke for each atom

Examples:

    compute 1 flow variable/atom myVar

Description:

Define a computation that calculates a formula for each atom in the group. The resulting values can be accessed by any command that uses per-atom computes, e.g. the dump custom command or fix ave/spatial command or fix ave/atom command.

The value of the variable evaluation will be 0.0 for atoms not in the specified compute group.

The formula is defined by the variable atom 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

If the dump line were replaced by

    fix 1 flow ave/spatial 100 1000 z lower 2.0 ke.profile compute ke

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, fix ave/spatial

Default: none