[petsc-dev] sor smoothers

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:
> We should add MatResidual() to the basic Mat methods (note this is the
> same as MatMultSub() if we had such a thing) then all the many places
> in PETSc where we have MatMult(); MatAXPY/AYPX(); 

* VecAXPY

> can be replace with that one call and PCMGSetResidual() and
> PCMGResidualDefault() would just disappear.  We could have
> MatResidual_Default() that did the usual MatMult followed by VecAYPX()
> but each Mat implementation can implement an optimized one if they
> want.

An alternative would be to add a scalar parameter to MatMultAdd.

To make the caching safe, the Mat impl would record the State of the Vec
for which it was caching a triangular application.

Perhaps PetscObjects should get a 64-bit unique ID assigned by a global
counter, or even a slightly longer hash of information that should never
repeat.  Caching the pointer leaves the ABA problem.
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