How to know the all the ranks that are part of a group in MPI outside that group?

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Is there a way for a rank 'R' to know the processes in a particular MPI_Group 'Grp', despite 'R' not belonging to 'Grp'. I want to do it without using any point to point communication calls, collective communication calls like Gather, Gatherv, Scatter etc and shared memory. Is it possible to use MPI_Group_translate_ranks for this purpose?

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Wesley Bland On

If an MPI process is not in a particular group, then it won't have a handle to be able to query it. In MPI, the only way you get handles to groups, communicators, etc. is to be part of the creation of that handle.

So to answer your question, no, there probably isn't a way to learn information about groups of which you are not a member.

That being said, your question is still rather unclear. You're asking to do something that I haven't ever heard of someone wanting to do before. If you can give a better demonstration of what exactly you're trying to do and why, you might get a better answer with another solution.