Generate an array from smaller arrays using MPI

Question

I would like to build a big array of dimensions (nx, ny, nz) starting from more smaller arrays of dimensions (nx, ny, nz/np), where np is the number of processors.

As I am new to MPI, I don't exactly know the best procedure. What I tried for now is this (fortran):

call mpi_sendrecv(u_small(nx, ny, nz/np), nx*ny*nz/np, rp, up, 1, u_tot(nx, ny,nz),nx*ny*nz, rp, down, 1, comm, status, ierr)

in which rp, comm and status are already properly defined and they're correct.

Thanks for the help

Victor Eijkhout · Accepted Answer · 2022-07-27 20:31:47Z

2

You seem vague on how MPI works. "build a big array" where? On one of the processes? Then you need to use MPI_Gather.

But I have to ask: why? MPI is partly motivated by the need for oodles of memory. (In a pre-multicore world, a process was a processor, so the more processes, the more processors, and the more memory.) So a good MPI program keeps all its data distributed, and you "big array" is something that exists only in your mind. Besides: if you have enough processes, that "big array" may not even fit the memory of a single process. So: why do you want to construct it explicitly to being with?

edited Jul 27, 2022 at 20:31

answered Jul 27, 2022 at 13:15

Victor Eijkhout

6,0002 gold badges29 silver badges31 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Ian Bush Over a year ago

Or possibly MPI_Gatherv. But I agree, keep things distributed - use of mpi_gather(v) usually indicates things are not being done in a good way.

Collectives™ on Stack Overflow

Generate an array from smaller arrays using MPI

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related