Hi, I'm trying to use MPI one-sided communication with sub-communicators. I've put my test code at the end of the email. It runs on 8 processors, creates two communicators, makes a window on the communicators, then tries to do some one-sided communication. I can use groups OR windows without a problem, but when I use them together (in the test code) I get a coredump from the first 4 tasks. I think the one-sided communication may be using the local rank in the sub-communicator (mpi_comm_grid) as if it is the global rank in mpi_comm_world. I can run the test code ok using open-mpi, but not mpich2. I might be missing something obvious. Thanks for your help, Helen ----- program test_group_win use mpi implicit none ! mpi integer :: rank, size, ierr, status(mpi_status_size) ! groups integer, parameter :: group_size = 4 integer :: group_members(group_size) integer :: group_all ! mpi_comm_world group integer :: subgroup integer :: mpi_comm_grid integer :: local_rank ! rank within subgroup ! window integer :: win integer ::bytesize !> size in bytes of each element in the window integer(KIND=MPI_ADDRESS_KIND) :: window_size pointer(aa, duplicate) real :: duplicate(*) integer(KIND=MPI_ADDRESS_KIND) :: target_disp !> displacement in window integer :: owner real :: result call mpi_init(ierr) call mpi_comm_size(mpi_comm_world, size, ierr) call mpi_comm_rank(mpi_comm_world, rank, ierr) ! create groups call mpi_comm_group(mpi_comm_world, group_all, ierr) if (rank < 4 ) then group_members = (/0,1,2,3/) else group_members = (/4,5,6,7/) endif call mpi_group_incl(group_all, group_size, group_members, subgroup, ierr) call mpi_comm_create(mpi_comm_world, subgroup, mpi_comm_grid, ierr) call mpi_comm_rank(mpi_comm_grid, local_rank, ierr) ! rank within group ! create window call mpi_type_size(mpi_real, bytesize, ierr) window_size = bytesize ! one element in the window aa = malloc(1) call MPI_ALLOC_MEM(window_size, mpi_info_null, aa, ierr) duplicate(1) = rank call mpi_win_create(duplicate, window_size, bytesize, MPI_INFO_NULL, mpi_comm_grid, win, ierr) ! grabbing data from rank above if (rank < 3 ) then owner = rank + 1 elseif (rank < 7) then owner = rank + 1 - 4 else owner = 0 endif print*, 'rank owner', rank, owner target_disp = 0 call mpi_win_lock(MPI_LOCK_SHARED, owner, 0, win, ierr) call mpi_get(result, 1, mpi_real, owner, target_disp, 1, mpi_real, win, ierr) call mpi_win_unlock(owner, win, ierr) print*, 'rank, result ', rank, result ! free window call mpi_win_free(win, ierr) call mpi_free_mem(duplicate, ierr) call mpi_finalize(ierr) end program test_group_win ----