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

Franck Houssen franck.houssen at inria.fr
Sun Dec 31 08:40:47 CST 2017 

Seems finally, I got it to work.
To get the options to work I had to call PetscOptionsBegin/End after/before PetscOptionsHead/Tail which is not what is done in the jacobi example: is this the right way to go ?

Franck

PetscErrorCode PCSetFromOptions_mypc(PetscOptionItems * PetscOptionsObject, PC pcPC) {
PetscOptionsHead
PetscOptionsBegin
... // PetscOptionsStringArray
PetscOptionsEnd
PetscOptionsTail


----- Mail original -----
> De: "Franck Houssen" <franck.houssen at inria.fr>
> À: "Barry F. Smith" <bsmith at mcs.anl.gov>
> Cc: "For users of the development version of PETSc" <petsc-dev at mcs.anl.gov>
> Envoyé: Dimanche 31 Décembre 2017 15:01:43
> Objet: Re: [petsc-dev] How to pass user data to a registered PC (PCRegister) ?
> 
> Using PCSHELL means calling:
>  - PCShellSetSetUp, PCShellSetApply, PCShellSetDestroy to set callbacks.
>  - PCShellSetContext/PCShellGetContext to get/set context in callbacks.
> 
> To go from PCSHELL to PCRegister, one need to:
>  - #include <petsc/private/pcimpl.h> // Access to PC data/struct.
>  - Set callbacks with pc->ops->...
>  - NO more use ANY shell methods (context, name), but, use pc->data instead.
>  - call PCRegister.
> 
> Correct ? Did I miss something ?
> 
> Seems I get things to work (without compose function).
> 
> The last problem I have is in the options: options are passed to
> PetscInitialize but not found in the database (I mimic'ed the jacobi
> example). Is there specific related to this ?
> 
> 
> ----- Mail original -----
> > De: "Franck Houssen" <franck.houssen at inria.fr>
> > À: "Barry F. Smith" <bsmith at mcs.anl.gov>
> > Cc: "For users of the development version of PETSc" <petsc-dev at mcs.anl.gov>
> > Envoyé: Samedi 30 Décembre 2017 17:12:09
> > Objet: Re: [petsc-dev] How to pass user data to a registered PC
> > (PCRegister) ?
> > 
> > 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
> > > 
> > > 
> > 
>

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