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

[Franck Houssen]

OK, on the highway now (bad ssh !), I'll try to check this out.

----- 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 18:21:48
> Objet: Re: [petsc-dev] How to pass user data to a registered PC (PCRegister) ?
> 
> 
> 
> > On Dec 28, 2017, at 10:34 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.
> 
>    Indeed it is exactly what it is meant for.  Please try to follow my recipe
>    and let us know when you get stuck.
> 
> 
> > 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);
> >> 

OK, I must provide/implement PCMypcSetDOFMultiplicities (add data to pc context) besides mypc_create: sounds logical.
Is this OK if PCMypcSetDOFMultiplicities is independent from mypc_create ? I guess yes.

>From what I remember/understand, I got lost here: from the jacobi example, mypc_create looks to be supposed (?) to call some kind of Petsc*ComposeFunction to associate PCMypcSetDOFMultiplicities to the pc (correct ?)... But, in the jacobi example, PCJacobiGetUseAbs_Jacobi is associated to PCJacobiGetUseAbs_C... Which turns out not to be implemented according to git grep ?! Got lost here (and looked for a way to pass user data directly to PCRegister): is PCMypcSetDOFMultiplicities supposed to be "attached/composed" or independent from the pc ?

>> git grep PCJacobiGetUseAbs_C
src/ksp/pc/impls/jacobi/jacobi.c:  ierr = PetscObjectComposeFunction((PetscObject)pc,"PCJacobiGetUseAbs_C",PCJacobiGetUseAbs_Jacobi);CHKERRQ(ierr);
src/ksp/pc/impls/jacobi/jacobi.c:  ierr = PetscUseMethod(pc,"PCJacobiGetUseAbs_C",(PC,PetscBool*),(pc,flg));CHKERRQ(ierr);

Sorry, for the short answer. Hope I succeeded to be clear enough.

> >> 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
> >> 
> >> 
> 
>