[petsc-dev] What should MatReset() do?

[Dmitry Karpeyev]

On Wed Feb 25 2015 at 10:56:30 PM Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> > On Feb 25, 2015, at 10:45 PM, Dmitry Karpeyev <karpeev at mcs.anl.gov>
> wrote:
> >
> > Since user callbacks, such as the one to compute the Jacobian, are now
> supposed to modify matrices in place, we need to provide the equivalent of
> MatReset() so that the user can do things like reset the sparsity pattern,
> etc. What should that call do?
> >
> > I assume it would keep the type, sizes and the block size of the matrix
> and reset everything else.   The impl-specific stuff is handled by
> MatDestroy(), but what about the generic data members?  I imagine that the
> structural properties, such as symmetry and others set with MatSetOption()
>
> Yes (this is in analogy to how KSPReset etc work, they clean out data
> objects but keep the options the user has selected for them)
>
> > as well as MatFactorType and MatStencilInfo should be preserved,
>
>
> Don't know about these.
>
> > while MatRedundant and the (Near)NullSpace have to go.
>
>   Yes
>
> > What about the logging info? num_ass?
>
>   Keep I think
> >  Do we increment nonzerostate or reset it?
>
> increment
>
> >  The PetscObject state?
>
> increment
>
Yes, these two need to be incremented, as I realized, to avoid a situation
where the same Mat object with a completely different structure has the
same state index as a previous incarnation.  The PC will think it doesn't
need to rebuild ...

>
> > I don't know what to do about the GPU pointers.
>
> I would clean those all out.
>
I'm not sure how -- isn't freeing these implementation-dependent?


> >
> > While MatReset() isn't yet available,  MatSetType(mat,newtype);
> MatSetType(mat,oldtype); should have the same effect,
> > but it doesn't, which to me is a bug
>
>    I agree it seems like a bug
>
> > and I'd like to fix it in maint.
> > It would be good, however, to do it "right" by answering the questions
> above.  Any opinions?
> >
> > Dmitry.
> >
>
>
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