lammps/doc/processors.txt

"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

processors command :h3

[Syntax:]

processors Px Py Pz :pre

Px,Py,Pz = # of processors in each dimension of a 3d grid :ul

[Examples:]

processors 2 4 4
processors * * 5
processors * 1 10 :pre

[Description:]

Specify how processors are mapped as a 3d logical grid to the global
simulation box, namely Px by Py by Pz.

Any of the Px, Py, Pz parameters can be specified with an asterisk
"*", which means LAMMPS will choose the number of processors in that
dimension.  It will do this based on the size and shape of the global
simulation box so as to minimize the surface-to-volume ratio of each
processor's sub-domain.

Since LAMMPS does not load-balance by changing the grid of 3d
processors on-the-fly, this command can be used to override the LAMMPS
default if it is known to be sub-optimal for a particular problem.
For example, a problem where the atom's extent will change
dramatically in a particular dimension over the course of the
simulation.

The product of Px, Py, Pz must equal P, the total # of processors
LAMMPS is running on.  For a "2d simulation"_dimension.html, Pz must
equal 1.  If multiple partitions are being used then P is the number
of processors in this partition; see "this
section"_Section_start.html#start_6 for an explanation of the
-partition command-line switch.

Note that if you run on a large, prime number of processors P, then a
grid such as 1 x P x 1 will be required, which may incur extra
communication costs.

[Restrictions:]

This command cannot be used after the simulation box is defined by a
"read_data"_read_data.html or "create_box"_create_box.html command.
It can be used before a restart file is read to change the 3d
processor grid from what is specified in the restart file.

[Related commands:] none

[Default:]

Px Py Pz = * * *