forked from lijiext/lammps
120 lines
4.4 KiB
Plaintext
120 lines
4.4 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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processors command :h3
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[Syntax:]
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processors Px Py Pz keyword args ... :pre
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Px,Py,Pz = # of processors in each dimension of a 3d grid :ulb,l
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zero or more keyword/arg pairs may be appended :l
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keyword = {part} :l
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{part} args = Psend Precv cstyle
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Psend = partition # (1 to Np) which will send its processor layout
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Precv = partition # (1 to Np) which will recv the processor layout
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cstyle = {multiple}
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{multiple} = Psend layout will be multiple of Precv layout in each dimension :pre
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:ule
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[Examples:]
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processors 2 4 4
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processors * * 5
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processors * * * part 1 2 multiple :pre
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[Description:]
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Specify how processors are mapped as a 3d logical grid to the global
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simulation box, namely Px by Py by Pz.
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Any of the Px, Py, Pz parameters can be specified with an asterisk
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"*", which means LAMMPS will choose the number of processors in that
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dimension. It will do this based on the size and shape of the global
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simulation box so as to minimize the surface-to-volume ratio of each
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processor's sub-domain.
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Since LAMMPS does not load-balance by changing the grid of 3d
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processors on-the-fly, this command can be used to override the LAMMPS
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default if it is known to be sub-optimal for a particular problem.
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For example, a problem where the atom's extent will change
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dramatically in a particular dimension over the course of the
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simulation.
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The product of Px, Py, Pz must equal P, the total # of processors
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LAMMPS is running on. For a "2d simulation"_dimension.html, Pz must
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equal 1. If multiple partitions are being used then P is the number
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of processors in this partition; see "this
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section"_Section_start.html#start_6 for an explanation of the
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-partition command-line switch.
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Note that if you run on a large, prime number of processors P, then a
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grid such as 1 x P x 1 will be required, which may incur extra
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communication costs.
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:line
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The {part} keyword can be useful when running in multi-partition mode,
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e.g. with the "run_style verlet/split"_run_style.html command. It
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specifies a dependency bewteen a sending partition {Psend} and a
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receiving partition {Precv} which is enforced when each is setting up
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their own mapping of the partitions processors to the simulation box.
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Each of {Psend} and {Precv} must be integers from 1 to Np, where Np is
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the number of partitions you have defined via the "-partition
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command-line switch"__Section_start.html#start_6.
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A "dependency" means that the sending partition will create its 3d
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logical grid as Px by Py by Pz and after it has done this, it will
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send the Px,Py,Pz values to the receiving partition. The receiving
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partition will wait to receive these values before creating its own 3d
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logical grid and will use the sender's Px,Py,Pz values as a
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constraint. The nature of the constraint is determined by the
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{cstyle} argument.
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For a {cstyle} of {multiple}, each dimension of the sender's processor
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grid is required to be an integer multiple of the corresponding
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dimension in the receiver's processor grid. This is a requirement of
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the "run_style verlet/split"_run_style.html command.
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For example, assume the sending partition creates a 4x6x10 grid = 240
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processor grid. If the receiving partition is running on 80
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processors, it could create a 4x2x10 grid, but it will not create a
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2x4x10 grid, since in the y-dimension, 6 is not an integer multiple of
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4.
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:line
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Note that you can use the "partition"_partition.html command to
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specify different processor grids for different partitions, e.g.
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partition yes 1 processors 4 4 4
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partition yes 2 processors 2 3 2 :pre
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IMPORTANT NOTE: If you use the "partition"_partition.html command to
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invoke different "processsors" commands on different partitions, and
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you also use the {part} keyword, then you must insure that both the
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sending and receiving partitions invoke the "processors" command that
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connects the 2 partitions via the {part} keyword. LAMMPS cannot
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easily check for this, but your simulation will likely hang in its
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setup phase if this error has been made.
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:line
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[Restrictions:]
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This command cannot be used after the simulation box is defined by a
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"read_data"_read_data.html or "create_box"_create_box.html command.
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It can be used before a restart file is read to change the 3d
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processor grid from what is specified in the restart file.
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[Related commands:] none
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[Default:]
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Px Py Pz = * * *
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