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### processors command

Syntax:

    processors Px Py Pz

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

Examples:

    processors 2 4 4
    processors * * 5
    processors * 1 10

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, Pz must equal 1. If multiple partitions are being used then P is the number of processors in this partition; see this section 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 or create_box 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 = * * *