Read a grid file in text format which lists the grid cell IDs to be used to construct a hierarchical grid that overalys the simulation domain defined by the create_box command. The grid can also be defined by the create_grid command.
The grid file can be written by the write_grid command in a previous simulation, or be created by some pre-processing tool. See Section 6.8 of the manual for a definition of hierarchical grids and grid cell IDs as used by SPARTA.
The specified file can be a text file or a gzipped text file (detected by a .gz suffix). See the write_grid command for a description of the format of the file.
The grid cell IDs read from the file to processors in a round-robin fashion, which means in general the set of cells a processor owns will not be contiguous in a geometric sense. They are thus assumed to be a "dispersed" assignment of grid cells to each processor.
IMPORTANT NOTE: See Section 6.8 of the manual for an explanation of clumped and dispersed grid cell assignments and their relative performance trade-offs. The balance_grid command can be used after the grid is read, to assign child cells to processors in different ways. The "fix balance" command can be used to re-assign them in a load-balanced manner periodically during a running simulation.
This command can only be used after the simulation box is defined by the create_box command.
To read gzipped grid files, you must compile SPARTA with the -DSPARTA_GZIP option - see Section 2.2 of the manual for details.