7.7.1. Example using MPI_ALLGATHER

The example in this section uses intra-communicators.

Example The all-gather version of Example Examples using MPI_GATHER and MPI_GATHERV. Using MPI_ALLGATHER, we will gather 100 ints from every MPI process in the group to every MPI process.

MPI_Comm comm; 
int gsize,sendarray[100]; 
int *rbuf; 
... 
MPI_Comm_size(comm, &gsize); 
rbuf = (int *)malloc(gsize*100*sizeof(int)); 
MPI_Allgather(sendarray, 100, MPI_INT, rbuf, 100, MPI_INT, comm); 

After the call, every MPI process has the group-wide concatenation of the sets of data.