pbdBASE (version 0.1-1)

OwnerShip: Determining Local Ownership of a Distributed Matrix

Description

aa

Usage

ownany(x, ..., dim, bldim, CTXT = 0)
  numroc(dim, bldim, ICTXT = 0, fixme = TRUE)

Arguments

x

distributed matrix

...

optional extra arguments

dim

global dimension

bldim

blocking dimension

ICTXT, CTXT

BLACS context

fixme

logical, controls correction of local dimension return

Details

For advanced users only. numroc() is a re-implementation at the R level of the ScaLAPACK subroutine NUMROC, which returns the local dimension of the matrix storage, i.e. the dimension for the Data slot of the distributed matrix on that process. The fixme= option, if TRUE, returns a minimum of 1 for each dimension. If fixme=FALSE, then values less than 1 for either dimension are possible, and in this case indicate a lack of local ownership of the global matrix. ownany() is a simple wrapper of numroc. The return is the answer to the question 'do I own any of the global matrix?'. Passing a distributed matrix is allowed, but often it is convenient to determine that information without even having a distributed matrix on hand. In this case, explicitly passing the appropriate information to the arguments dim=, bldim= (and CTXT= as necessary, since it defaults to 0) while leaving x missing will produce the desired result. See the examples below for more clarity. The return for each function is local.

See Also

BLACS, InitGrid

Examples

# 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()

# don't do this in production code
x <- matrix(1:16, ncol=4)
dx <- as.ddmatrix(x, bldim=2) 

iown <- ownany(dx)
comm.print(iown, all.rank=T)

iown <- ownany(dim=c(4, 4), bldim=c(2, 2), CTXT=0)
comm.print(iown, all.rank=T)

# but NOT
# ownany(c(4,4), c(2,2), 0)
# ^this will produce an error

finalize()