[petsc-dev] How to pass user data to a registered PC (PCRegister) ?

[Matthew Knepley]

On Thu, Dec 28, 2017 at 11:34 AM, Franck Houssen <franck.houssen at inria.fr>
wrote:

> ----- Mail original -----
> > De: "Barry F. Smith" <bsmith at mcs.anl.gov>
> > À: "Franck Houssen" <franck.houssen at inria.fr>
> > Cc: "For users of the development version of PETSc" <
> petsc-dev at mcs.anl.gov>
> > Envoyé: Jeudi 28 Décembre 2017 16:43:16
> > Objet: Re: [petsc-dev] How to pass user data to a registered PC
> (PCRegister) ?
> >
> >
> >    The register is for a new type of PC of which can have many
> instantiations
> >    at the same time.
>
> OK, I didn't get that that way ! I was looking for a way to plug "my" pc
> at the command line this way: -pc_type my_pc.
> I already call PCSetType(pc, PCSHELL) and PCShellSetName(pc, "my_pc"):
> maybe this already enables "-pc_type shell" or "-pc_type my_pc"... And I
> didn't know it ! :D I'll try that.
>
> I was looking for a way to integrate "my" (external) pc as any other
> regular/existing petsc pc (bjacobi, ...) like a kind of plugin but still
> integrated to the cmd line: I believed PCRegister was meant for that.
> Not sure if this is actually possible/enabled by the API.


Yes, this is how PCRegister works. Barry is also right that you would put
your information directly in the impl struct for my_pc. Then you write a
specific interface
function for that data, e,g, PCJacobiSetUseAbs(). Here is our canonical
example:


https://bitbucket.org/petsc/petsc/src/4de00746c5d9ba3d09a7cdd5c64a5cab5c60cbfa/src/ksp/pc/impls/jacobi/jacobi.c?at=master&fileviewer=file-view-default

There is a bunch of documentation at the top of that file.

  Thanks,

     Matt


> > For example
> >
> >     PCRegister("mypctype",mypc_create);
> >
> >     KSPCreate(&ksp1);
> >     KSPCreate(&ksp2);
> >
> >     KSPGetPC(ksp1,&pc1);
> >     KSPGetPC(ksp2,&pc2);
> >
> >     You don't want pc1 and pc2 to have the same dof multiplicities,
> domain
> >     intersections etc since they are associated with completely different
> >     linear systems and presumably meshes etc.
> >
> >
> >      Presumably you want each of pc1, pc2, to have their own version of
> the
> >      data so you need to stick it directly in the PC, for example
> >
> >    PCMypcSetDOFMultiplicities(pc1,stuff);
> >   PCMypcSetDOFMultiplicities(pc2,otherstuff);
> >
> > You write as many of these Set() functions as you need for your PCtype.
> You
> > store the data inside the PC_Mypc data structure you create with
> > mypc_create(). Look at PCCreate_Jacobi() and PCJacobiSetType for the
> > pattern.
> >
> >    Barry
> >
> >
> > > On Dec 28, 2017, at 9:34 AM, Franck Houssen <franck.houssen at inria.fr>
> > > wrote:
> > >
> > > How to pass user data to a registered PC (PCRegister) ?
> > >
> > > At first, I expected the signature would be "PetscErrorCode
> > > PCRegister(const char sname[],PetscErrorCode (*function)(PC, void *))"
> but
> > > it turns out to be "PetscErrorCode PCRegister(const char
> > > sname[],PetscErrorCode (*function)(PC))"
> > >
> > > I try to integrate a PC that needs A but also other informations (dof
> > > multiplicities, domain intersections that the user must provide). I
> guess
> > > I can get A with PCGetOperators in the setup callback of the PC. But
> still
> > > not sure how to pass the other informations if I get to use
> PCRegister. I
> > > looked a few examples in the bitbucket (jacobi:
> > > src/ksp/ksp/examples/tutorials/ex12.c and src/ksp/pc/impls/jacobi/
> jacobi.c
> > > + SOR: src/ksp/pc/impls/sor/sor.c)... But didn't get any real relevant
> > > answer and feel a bit lost among the numerous pc !...
> > >
> > > The idea is: for now I use PCSetType(pc, PCSHELL) and PCShellSetContext
> > > with a context who knows the extra needed informations which is "not so
> > > handy" (that's OK as for now I am both the user and the PC provider).
> I'd
> > > like to package this in a more convenient way (a unique and "simple"
> call
> > > to PCRegister) to decouple the user from the PC machinery.
> > >
> > > Franck
> >
> >
>



-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
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