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

[Franck Houssen]

----- 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.

> 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
> 
>