Rmpi (version 0.7-2.1)

mpi.gather: MPI_Gather, MPI_Gatherv, MPI_Allgather, and MPI_Allgatherv APIs

Description

mpi.gather and mpi.gatherv (vector variant) gather each member's message to the member specified by the argument root. The root member receives the messages and stores them in rank order. mpi.allgather and mpi.allgatherv are the same as mpi.gather and mpi.gatherv except that all members receive the result instead of just the root.

Usage

mpi.gather(x, type, rdata, root = 0, comm = 1) 
mpi.gatherv(x, type, rdata, rcounts, root = 0, comm = 1) 
mpi.allgather(x, type, rdata, comm = 1) 
mpi.allgatherv(x, type, rdata, rcounts, comm = 1)

Value

For mpi.gather or mpi.gatherv, it returns the gathered message for the root member. For other members, it returns what is in rdata, i.e., rdata (or rcounts) is ignored. For mpi.allgather or

mpi.allgatherv, it returns the gathered message for all members.

Arguments

x

data to be gathered. Must be the same type.

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 and big enough to include all message gathered.

rcounts

int vector specifying the length of each message.

root

rank of the receiver

comm

a communicator number

Author

Hao Yu

Details

For mpi.gather and mpi.allgather, the message to be gathered must be the same dim and the same type. The receive buffer can be prepared as either integer(size * dim) or double(size * dim), where size is the total number of members in a comm. For mpi.gatherv and mpi.allgatherv, the message to be gathered can have different dims but must be the same type. The argument rcounts records these different dims into an integer vector in rank order. Then the receive buffer can be prepared as either integer(sum(rcounts)) or double(sum(rcounts)).

References

https://www.open-mpi.org/

See Also

mpi.scatter, mpi.scatterv.

Examples

# \donttest{
#Need 3 slaves to run properly
#Or use mpi.spawn.Rslaves(nslaves=3)
#mpi.bcast.cmd(id <-mpi.comm.rank(.comm), comm=1)
#mpi.bcast.cmd(mpi.gather(letters[id],type=3,rdata=string(1)))

#mpi.gather(letters[10],type=3,rdata=string(4))

# mpi.bcast.cmd(x<-rnorm(id))
# mpi.bcast.cmd(mpi.gatherv(x,type=2,rdata=double(1),rcounts=1))
# mpi.gatherv(double(1),type=2,rdata=double(sum(1:3)+1),rcounts=c(1,1:3))

#mpi.bcast.cmd(out1<-mpi.allgatherv(x,type=2,rdata=double(sum(1:3)+1),
#		rcounts=c(1,1:3)))
#mpi.allgatherv(double(1),type=2,rdata=double(sum(1:3)+1),rcounts=c(1,1:3))
# }