> 2/32: The term "derived from" has a different meaning in MPI than what
> I think you want over here. I think you want it to be anything
> "datatype" was constructed out of. (Even the wording in my sentence is
> not precise.) Is it necessary to allow a derived datatype constructed
> from the datatype passed in the read/write function? That can be taken
> care of using count.
What I intended here was to permit an implementation to send a
datatype that was constructed out of a type that the user passed
to a read or write. For example, an implementation might build
a contiguous type using the datatype and the count, rather
than compute the tiling itself. I didn't mean that the
implementation might cut a datatype into pieces and pass in
pieces, although I guess that could be permitted too. So
according to my understanding of how MPI uses "derived," I
think I said what I meant. Whether what I meant is right is
another question...
John