[petsc-dev] MATCOMPOSITE as fallback for matrix-matrix multiplication

[Jed Brown]

Matthew Knepley <knepley at gmail.com> writes:

> On Mon, Mar 11, 2019 at 6:59 PM Jed Brown via petsc-dev <
> petsc-dev at mcs.anl.gov> wrote:
>
>> One could imagine PETSc written so that all Mat operations like
>> transpose and products return lazy representations, with a method that
>> makes it explicit.  Would eliminate all the Transpose variants in the
>> matrix products, for example, and enable an implementation to choose
>> order of operations for chained products.
>>
>
> Didn't Liz Jessup (and others) do a BLAS subset this way in order to
> fuse operations? Did these not catch on because it is a maintenance
> burden, or just that you don't get a big win?

I can ask.  I suspect it's mostly lack of distribution.  Nobody uses a
library that only provides that feature, so it needs to be in something
popular to get used.  Paolo has also done stuff like that (choosing
(approximately) optimal order of operations for complex matrix
expressions).