init.grid(NPROW, NPCOL, ICTXT, ..., quiet = FALSE)
blacs_gridinit(ICTXT, NPROW, NPCOL, ..., quiet = FALSE).pbdBASEEnv environment. See Details
section.blacs_gridinit() is for experienced users only. It is a shallow
wrapper of the BLACS routine BLACS_GRIDINIT, 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.
# Save code in a file "demo.r" and run with 2 processors by
# > mpiexec -np 2 Rscript demo.r
library(pbdBASE, quiet = TRUE)
init.grid()
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