Question

The question says it all. I have three communicators(Groups are also available). Now I want to call the a function just for one communication subset. That is mask the function for other subsets. Is this possible or should I explicitly right a loop and check for the existence of the current process in the group and then call the function.

Thanks,

Answer 1

There is no way to call a function over all members of a subcommunicator apart from abusing user-defined reduction operators in MPI_Allreduce(). The cleanest thing to do is:

int group_rank;
// Test if current process belongs to "group"
MPI_Group_rank(group, &group_rank);
if (group_rank != MPI_UNDEFINED)
   call_the_function();