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

[Dmitry Karpeev]

On Tue, Sep 20, 2011 at 5:41 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> On Sep 20, 2011, at 2:06 PM, Jed Brown wrote:
>
> > 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.
>
>    MPI has its own kinds of constructs for doing things; you could argue
> they suck ...
>
> > 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.
>
>   I wanted something that would bark like crazy and attack burglars at my
> house but I also wanted it to cuddle up on my lap and purr to me so I made a
> doat.
>
> The problem I see with a general scatter is that it has to operate on
"laid-out" objects (so that, among other things, the scatter knows where to
stick the things that arrive).  Currently, only Vec and Mat have layouts.

Dmitry.
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