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

Sat Dec 30 10:12:09 CST 2017

Don't get the link. I'll try first with independent function (no compose) and see if this can work at least for a start.

Franck

----- 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: Vendredi 29 Décembre 2017 17:55:30
> Objet: Re: [petsc-dev] How to pass user data to a registered PC (PCRegister) ?
> 
> 
> 
> > On Dec 29, 2017, at 9:03 AM, Franck Houssen <franck.houssen at inria.fr>
> > wrote:
> > 
> > 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...
> 
>   the _C name is a string name that is used by PETSc to "find" the correct
>   function pointer which is PCJacobiGetUseAbs_Jacobi. There is no
> _C function.

?!

> 
> > 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 ?
> 
>    composed.
> 
> > 
> >>> 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.
> 
>    Just copy jacobi.c and start converting it over to your names and needs
>    and you'll see it is actually really straightforward and not as
>    complicated as you think it is.
> 
>    Barry
> 
> > 
> >>>> 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
> 
> 