pbdMPI (version 0.2-3)

gather-method: A Rank Gathers Objects from Every Rank

Description

This method lets a rank gather objects from every rank in the same communicator. The default return is a list of length equal to `comm size'.

Usage

gather(x, x.buffer = NULL, x.count = NULL, displs = NULL,
         rank.dest = .SPMD.CT$rank.root, comm = .SPMD.CT$comm,
         unlist = .SPMD.CT$unlist)

Arguments

x

an object to be gathered from all ranks.

x.buffer

a buffer to hold the return object which probably has `size of x' times `comm size' with the same type of x.

x.count

a vector of length `comm size' containing all object lengths.

displs

c(0L, cumsum(x.count)) by default.

rank.dest

a rank of destination where all x gather to.

comm

a communicator number.

unlist

if unlist the return.

Value

• If rank.dest == comm.rank(comm), then a list of length `comm size' is returned by default. Otherwise, NULL is returned.

Details

All x on all ranks are likely presumed to have the same size and type.

x.buffer, x.count, and displs can be NULL or unspecified. If specified, the type should be one of integer, double, or raw specified correctly according to the type of x.

If x.count is specified, then the spmd.gatherv.*() is called.

References

Programming with Big Data in R Website: http://r-pbd.org/

See Also

gather(), allreduce(), reduce().

Examples

### Save code in a file "demo.r" and run with 2 processors by
### SHELL> mpiexec -np 2 Rscript demo.r

### Initial.
library(pbdMPI, quietly = TRUE)
init()
.comm.size <- comm.size()
.comm.rank <- comm.rank()

### Examples.
N <- 5
x <- (1:N) + N * .comm.rank
y <- gather(matrix(x, nrow = 1))
comm.print(y)
y <- gather(x, double(N * .comm.size))
comm.print(y)

### Finish.
finalize()