Rmpi (version 0.6-9)

mpi.scatter: MPI\_Scatter and MPI\_Scatterv APIs

Description

mpi.scatter and mpi.scatterv are the inverse operations of mpi.gather and mpi.gatherv respectively.

Usage

mpi.scatter(x, type, rdata, root = 0,  comm = 1) 
mpi.scatterv(x, scounts, type, rdata, root = 0, comm = 1)

Arguments

x

data to be scattered.

type

1 for integer, 2 for double, and 3 for character. Others are not supported.

rdata

the receive buffer. Must be the same type as the sender

scounts

int vector specifying the block length inside a message to be scattered to other members.

root

rank of the receiver

comm

a communicator number

Value

For non-root members, mpi.scatter or scatterv returns the scattered message and ignores whatever is in x (or scounts). For the root member, it returns the portion belonging to itself.

Details

mpi.scatter scatters the message x to all members. Each member receives a portion of x with dim as length(x)/size in rank order, where size is the total number of members in a comm. So the receive buffer can be prepared as either integer(length(x)/size) or double(length(x)/size). For mpi.scatterv, scounts counts the portions (different dims) of x sent to each member. Each member needs to prepare the receive buffer as either integer(scounts[i]) or double(scounts[i]).

References

http://www.openmpi.org/

See Also

mpi.gather, mpi.gatherv.

Examples

# NOT RUN {
#Need 3 slaves to run properly
#Or run  mpi.spawn.Rslaves(nslaves=3)
  num="123456789abcd"
  scounts<-c(2,3,1,7)
  mpi.bcast.cmd(strnum<-mpi.scatter(integer(1),type=1,rdata=integer(1),root=0))
  strnum<-mpi.scatter(scounts,type=1,rdata=integer(1),root=0)
  mpi.bcast.cmd(ans <- mpi.scatterv(string(1),scounts=0,type=3,rdata=string(strnum),
					root=0))
  mpi.scatterv(as.character(num),scounts=scounts,type=3,rdata=string(strnum),root=0)
  mpi.remote.exec(ans)
# }