Difference between MPI_Alltoall and MPI_Allgather

[s***@web.de]

Hi there!

I've been trying (and failing) to find out what exactly the difference
between MPI_Alltoall and MPI_Allgather is. Can anybody explain please?

Thanks, Steffen

[Michael Hofmann]

Post by s***@web.de
Hi there!
I've been trying (and failing) to find out what exactly the difference
between MPI_Alltoall and MPI_Allgather is. Can anybody explain please?

MPI_Alltoall: every process sends an *individual* message to every other
process. With p processes, there are p*p different messages. The result (=
the received messages) is different on all processes.

MPI_Allgather: every process sends the *same* message to every other
process. With p processes, there are p different messages. The result is
the same on all processes.


Michael