On Friday, 26 August 2016, Steven Dargaville <dargaville.ste...@gmail.com> wrote:
> Hi Dave > > Thanks for the response. I'm actually using fortran and I wasn't sure that > PetscObjectComposeFunction would be accessible, and if so, what sort of > fortran magic I might need to call this function (possibly an interface, > with or without c_opt). > > Do you know if it is possible to call that routine directly from fortran? > I don't know. I'll have appeal to the other petsc users for an answer to these questions. Thanks, Dave > Thanks > Steven > > On Fri, Aug 26, 2016 at 1:35 PM, Dave May <dave.mayhe...@gmail.com > <javascript:_e(%7B%7D,'cvml','dave.mayhe...@gmail.com');>> wrote: > >> >> >> On 26 August 2016 at 14:34, Dave May <dave.mayhe...@gmail.com >> <javascript:_e(%7B%7D,'cvml','dave.mayhe...@gmail.com');>> wrote: >> >>> >>> >>> On 26 August 2016 at 14:14, Steven Dargaville < >>> dargaville.ste...@gmail.com >>> <javascript:_e(%7B%7D,'cvml','dargaville.ste...@gmail.com');>> wrote: >>> >>>> Hi all >>>> >>>> I'm just wondering if there is any plans in the future for >>>> MatGetDiagonalBlock to support shell matrices by registering a >>>> user-implemented MATOP? MatGetDiagonal supports MATOP, but the block >>>> version of this does not. >>>> >>>> I found a previous query on the user list which touched on this and >>>> mentioned that it would be easy to add: >>>> >>>> http://lists.mcs.anl.gov/pipermail/petsc-users/2011-May/008700.html >>>> >>>> I have implemented a matrix-free multigrid algorithm using shell >>>> operations in PETSc, and it would be very convenient to be able to provide >>>> a local shell Mat so I could apply local GMRES (or other matvec-based >>>> solvers) as a local block smoother. >>>> >>> >>> It looks like the thing you need to do is use >>> PetscObjectComposeFunction() and not MatShellSetOperation() >>> >>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/ >>> Sys/PetscObjectComposeFunction.html#PetscObjectComposeFunction >>> >>> with your MatShell object. >>> >>> That is, instead of calling MatShellSetOperation(), call >>> ierr = PetscObjectComposeFunction(myshell,"MatGetDiagonalBlock_C", >>> MatGetDiagonalBlock_MyShell);CHKERRQ(ierr); >>> >> >> Oops - I forgot the cast, the above should be >> >> ierr = PetscObjectComposeFunction((PetscObject)myshell,"MatGetDiago >> nalBlock_C", MatGetDiagonalBlock_MyShell);CHKERRQ(ierr); >> >> >>> >>> where MatGetDiagonalBlock_MyShell is a function pointer to your method >>> to get the diagonal block. >>> >>> Important detail is that you don't change the string >>> "MatGetDiagonalBlock_C". The method MatGetDiagonalBlock() does a function >>> pointer query using this string. See >>> http://www.mcs.anl.gov/petsc/petsc-current/src/mat/interface >>> /matrix.c.html#MatGetDiagonalBlock >>> >>> >>> Thanks >>> Dave >>> >>> >>> >>> >>> >>> >>>> >>>> Thanks! >>>> Steven >>>> >>>> >>>> >>> >> >
