[petsc-dev] Suggestions for MatProductCreate()

[Patrick Sanan]

You can put whatever message you like when you deprecate the function, so
perhaps here you could leave the old functions and say something like

PETSC_DEPRECATED_FUNCTION("Use X() and Y() (since version 3.13)")
PetscErrorCode <https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PetscErrorCode.html#PetscErrorCode>
OldFunction();


and you can leave the man page but change the "level" to "deprecated",
which I don't think is usually done for simpler deprecations that are just
name changes, that look like this:

    PETSC_DEPRECATED_FUNCTION("Use DMLocalToLocalBegin() (since version
3.5)") PETSC_STATIC_INLINE PetscErrorCode DMDALocalToLocalBegin(DM dm,Vec
g,InsertMode mode,Vec l) {return DMLocalToLocalBegin(dm,g,mode,l);}

(P.S. Once the web-based dev manual is merged, we could (easily, by editing
an .rst file on the web) make a separate section on deprecation since right
now it's buried in the style/usage guide, and doesn't have an example of
deprecating macros:
https://docs.petsc.org/en/psanan-docs-sphinx-dev-manual/developers/style.html#usage-of-petsc-functions-and-macros
)

Am Mo., 23. März 2020 um 15:56 Uhr schrieb Satish Balay via petsc-dev <
petsc-dev at mcs.anl.gov>:

> On Mon, 23 Mar 2020, hzhang--- via petsc-dev wrote:
>
> > Lisandro:
> >
> > > * Please consider fixing MatProductCreate(A,B,C,&D) to take ownership
> > > (that is, increase reference count) of the A,B, and the (optional) C
> > > matrices provided as arguments. Otherwise it is way easy to get into
> the
> > > dangling pointer trap.
> > >
> > Can you give me a simple example of " get into the dangling pointer
> trap"?
> > We do not use reference count to keep track of A, B for Mat-Mat
> operations
> > in the current and previous versions.
> >
> > >
> > > * A thing also missing in the new API is a way to "cleanup" the A,B,C
> > > references, something MatProductReset(D) to get rid of (deallocates)
> the
> > > internal "product" context, thus removing  from D the references to
> A,B,C.
> > > This would be useful if you just want to compute JUST the symbolic
> product,
> > > I'm using that in some code to compute the nonzero pattern of A^2.
> > >
> > Again, giving an example would help me understand. If you just want
> > the  symbolic product, you can call
> > MatProductCreate()
> > MatProductSetType()
> > MatProductSetFromOptions()
> > MatProductSymbolic().
> > This is equivalent to previous MatMatMultSymbolic(), and is used in some
> > routines of PETSc.
> >
> > >
> > > * It should be also considered to provide backward compatibility
> > > PETSC_DEPRECATED calls to the previous MatMatMultSymbolic()
> > > and MatMatMultNumeric(). It looks like it would be trivial to do,
> though I
> > > may be getting it wrong because I have not looked at all the details.
> > >
> >  MatMatMultSymbolic/Numeric() are not recommended for users, and few
> > developers ever used them.  I only see one or two PETSc subroutines call
> > them. I do not think we need provide backward compatibility
> > PETSC_DEPRECATED calls for 6 pairs of such routines.
>
> If there is a simple map from old API to new API [just new names, or
> reorder arguments] - we should include the old API with PETSC_DEPRECATED
>
> Alternative is PETSC_DEPRECATED with some error statement? Jed will know
> better..
>
>
> Satish
>
> >
> > Hong
> >
>
>
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