[petsc-dev] use of hash table vs array in various places in PETSc

[Jed Brown]

On Tue, Sep 20, 2011 at 19:14, Barry Smith <bsmith at mcs.anl.gov> wrote:

>  is a strange combination of PETSc types and MPI types and PETSc styles and
> MPI styles. The right way to think about what you want is purely in an MPI
> style.


I agree that it would naturally belong at the MPI level. I wrote it this way
because IS is a useful thing and MPI doesn't have any such object. In
particular, an aggregate MPI_Datatype encodes the type of each entry, but
it's useful to be able to push ints through the same pipes as floats, so
we'd end up producing an IS-like thingy in this MPI-add-on layer (or have a
rather complicated interface with different creation functions for various
combinations). I want the same scatter to be able to move different types
(to amortize setup and guarantee consistency), so it's not good enough to
specify all the types at the time it's created.
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