Manages the creation of BLACS context grids.
init.grid(NPROW, NPCOL, ICTXT, quiet = FALSE)number of process rows. Can be missing; see details.
number of process columns. Can be missing; see details.
BLACS context number.
logical; controls whether or not information about grid size should be printed.
Silently returns 0 when successful. Additionally, several variables
are created in the .pbdBASEEnv environment. See Details section.
blacs_init() is for experienced users only. It is a shallow
wrapper of the BLACS routine BLACS_INIT, with the addition of
creating the .__blacs_gridinfo_ICTXT objects, as described below.
The remainder of this section applies only to init.grid().
If ICTXT is missing, three variables will be created in the
.pbdBASEEnv environment:
.__blacs_gridinfo_0
.__blacs_gridinfo_1
.__blacs_gridinfo_2
These variables store the BLACS process grid information for the BLACS
context corresponding to the trailing digit of the variable. Most users
should invoke init.grid() in this fashion, namely with ICTXT missing,
and only do so once.
Contexts 0, 1, and 2 are reserved. Additional custom contexts are possible to create, but they must be integers >= 3.
Context 0 is the ``full'' process grid of NPROW by NPCOL
processes; contexts 1 is the process grid consisting of 1 process row and
NPROW*NPCOL processes columns; context 2 is the process grid
consisting of NPROW*NPCOL processes rows and 1 process column.
These contexts can be redundant depending on the number of prcesses
available.
BLACS contexts have important internal use, and advanced users familiar with ScaLAPACK might find some advantage in directly manipulating these process grids. Most users should not need to directly manage BLACS contexts, in this function or elsewhere.
If the NPROW and NPCOL values are missing, then a best process
grid will be chosen for the user based on the total available number of
processes. Here ``best'' means as close to a square grid as possible.
The variables .__blacs_gridinfo_ICTXT are just storage mechanisms to
avoid needing to directly invoke the BLACS routine BLACS_GRIDINFO.
Additionally, another variable is created in the .pbdBASEEnv
environment, namely .__blacs_initialized. Its existence is to alert
finalize() to shut down BLACS communicators, if necessary, to prevent
memory leaks.
# NOT RUN {
spmd.code = "
suppressMessages(library(pbdBASE))
init.grid()
finalize()
"
pbdMPI::execmpi(spmd.code = spmd.code, nranks = 2L)
# }
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