[petsc-users] Why use MATMPIBAIJ?

[Mark Adams]

>
>
> I used it for PyLith and saw this. I did not think any AMG had scalable
> setup time.
>
>
OK, I am guessing it was scaling poorly, weak scaling, but it was sublinear
after some saturation at the beginning.

I have not done a weak scaling study on matrix setup (RAP primarily) ever,
but I did on Prometheus in the GB work.  Prometheus' RAP  was pretty simple
also and PETSc's is probably faster, and hence may look less scalable.  I
don't think there is anything fundamentally unscalable about RAP, it is
just a complicated algorithm and we have never gotten around to doing all
the things that we would like to do with it.
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