This may be a silly question, but the reason

I'm asking is to obtain a fairly definitive answer.

Basically, does MPICH have data structures

which are of size:

1) O(N)

2) O(N^2)

Where N is the size of MPI_COMM_WORLD ?

My initial guess would be no, because there

exist machines (Mira) for which it is not

possible to store N^2 bytes, and even N bytes

becomes an issue.

I understand there are MPI functions (MPI_alltoall) one can

call that by definition will require at least O(N) memory,

but supposing one does not use these, would the internal

MPICH systems still have this memory complexity ?

Thank you for looking at this anyway