From: George Bosilca <bosi...@icl.utk.edu>
First and foremost the two datatype markers (MPI_LB and MPI_UB) have been
deprecated from MPI 3.0 for exactly the reason you encountered. Once a
datatype is annotated with these markers, they are propagated to all
derived types, leading to an unnatural datatype definition. This behavior
is enforced by the definition of the typemap specified by the equation on
Section 4.1 page 105 line 18. Unfortunately, the only way to circumvent
this issue, is to manually set the UB to all newly created datatypes.
I see I should have directly checked the specification to see what the
expected behavior was, instead of relying on (apparently over-)
simplified summaries from web searches and books. Thanks for the
pointer!
I'd wondered if this was a fixable bug, but it looks like that
equation dates back to at *least* 1994 and the MPI-1.0 spec; clearly
the only thing to do was deprecate and replace the API rather than
breaking old user code to enforce the "right" behavior instead.
Thus, to fix your datatype composition you just have to add an explicit
MPI_LB (set to 0) when calling the MPI_Type_struct on your second struct
datatype.
I'd managed to hit on this solution by guesswork, but it's quite a
relief to know that its correctness is actually mandated by the MPI
standand not just my dumb luck.
Thanks again,
---
Roy Stogner
