Gather¶

Gather works opposite to scatter. And it essentially captures data from several processes to the assigned process.

from mpi4py import MPI
import numpy as np

comm = MPI.COMM_WORLD
size = comm.Get_size()
rank = comm.Get_rank()

numDataPerRank = 10
sendbuf = np.linspace(rank*numDataPerRank+1,(rank+1)*numDataPerRank,numDataPerRank)
print('Rank: ',rank, ', sendbuf: ',sendbuf)

recvbuf = None
if rank == 0:
    recvbuf = np.empty(numDataPerRank*size, dtype='d')

comm.Gather(sendbuf, recvbuf, root=0)

if rank == 0:
    print('Rank: ',rank, ', recvbuf received: ',recvbuf)