Let me also add a minimal example (relying only on petsc), which leads
to the same error message on my machine. Again, what I'm trying to do is
very simple:
1. MatCreateShell => Initialize Mat :: F
2. MatShellSetContext => set the context of F to ctxF (looking at the
petsc source code, this call actually seems to be superfluous, but
nevermind)
3. MatShellGetContext => get the pointer ctxF_pt to point to the matrix
context
I'm getting an error message in the third step.
[0]PETSC ERROR: --------------------- Error Message
--------------------------------------------------------------
[0]PETSC ERROR: Null argument, when expecting valid pointer
[0]PETSC ERROR: Null Pointer: Parameter # 2
Again, thanks for your help!
Cheers,
Samuel
On 12/11/2017 07:41 PM, Samuel Lanthaler wrote:
Dear petsc-/slepc-users,
I have been trying to understand matrix-free/shell matrices in PETSc
for eventual use in solving a non-linear eigenvalue problem using
SLEPC. But I seem to be having trouble with calls to
MatShellGetContext. As far as I understand, this function should
initialize a pointer (second argument) so that the subroutine output
will point to the context associated with my shell-matrix (let's say
of TYPE(MatCtx))? When calling that subroutine, I get the following
error message:
[0]PETSC ERROR: --------------------- Error Message
--------------------------------------------------------------
[0]PETSC ERROR: Null argument, when expecting valid pointer
[0]PETSC ERROR: Null Pointer: Parameter # 2
In my code, the second input argument to the routine is a null-pointer
of TYPE(MatCtx),POINTER :: arg2. Which the error message appears to be
unhappy with. I noticed that there is no error message if I instead
pass an object TYPE(MatCtx) :: arg2 to the routine... which doesn't
really make sense to me? Could someone maybe explain to me what is
going on, here?
Just in case, let me also attach my concrete example code (it is
supposed to be a Fortran version of the slepc-example in
slepc-3.8.1/src/nep/examples/tutorials/ex21.c). I have added an extra
call to MatShellGetContext on line 138, after the function and
jacobian should supposedly have been set up.
Thanks a lot for your help!
Cheers,
Samuel
! ----------------------------------------------------
! user-defined context
! ----------------------------------------------------
MODULE solver_context
#include "petsc/finclude/petsc.h"
! ------
USE petscsys
USE petscmat
! ------
IMPLICIT NONE
TYPE :: MatCtx
PetscScalar :: lambda,kappa
PetscReal :: h
END TYPE MatCtx
END MODULE solver_context
MODULE solver_context_interfaces
USE solver_context
IMPLICIT NONE
! ----------------------------------------------------
INTERFACE MatCreateShell
! --------------
SUBROUTINE MatCreateShell(comm,mloc,nloc,m,n,ctx,mat,ierr)
USE solver_context
TYPE(MPI_COMM) :: comm
PetscInt :: mloc,nloc,m,n
TYPE(MatCtx) :: ctx
Mat :: mat
PetscErrorCode :: ierr
END SUBROUTINE MatCreateShell
END INTERFACE MatCreateShell
! ----------------------------------------------------
! ----------------------------------------------------
INTERFACE MatShellSetContext
! --------------
SUBROUTINE MatShellSetContext(mat,ctx,ierr)
USE solver_context
Mat :: mat
TYPE(MatCtx) :: ctx
PetscErrorCode :: ierr
END SUBROUTINE MatShellSetContext
END INTERFACE MatShellSetContext
! ----------------------------------------------------
! ----------------------------------------------------
INTERFACE MatShellGetContext
! --------------
SUBROUTINE MatShellGetContext(mat,ctx,ierr)
USE solver_context
Mat :: mat
TYPE(MatCtx), POINTER :: ctx
PetscErrorCode :: ierr
END SUBROUTINE MatShellGetContext
END INTERFACE MatShellGetContext
! ----------------------------------------------------
END MODULE solver_context_interfaces
! ----------------------------------------------------
! main program
! ----------------------------------------------------
PROGRAM main
#include "petsc/finclude/petsc.h"
! ------
USE petscsys
USE petscmat
! ------
USE solver_context
IMPLICIT NONE
Mat :: F
TYPE(MatCtx) :: ctxF
TYPE(MatCtx),POINTER :: ctxF_pt
PetscErrorCode :: ierr
PetscInt :: n=128
!
CALL PetscInitialize(PETSC_NULL_CHARACTER,ierr)
!
ctxF%lambda = 0.0d0
CALL MatCreateShell(PETSC_COMM_WORLD,n,n,n,n,ctxF,F,ierr)
CALL MatShellSetContext(F,ctxF,ierr)
PRINT*,'ctxF%lambda = ',ctxF%lambda
CALL MatShellGetContext(F,ctxF_pt,ierr)
PRINT*,'ctxF_pt%lambda = ',ctxF_pt%lambda
!
CALL PetscFinalize(ierr)
END PROGRAM main
