[petsc-users] Fortran 77 VecGetArray problems

[Barry Smith]

> On Nov 20, 2014, at 9:19 PM, Valerio Grazioso <graziosov at libero.it> wrote:
> 
> Dear Petsc Users,
> I’m trying to write a simple parallel linear solver (A*x=q) in fortran 77 with Petsc.
> I managed to Setup a MPIAIJ matrix A  and a VecMPI qvec
> then the KSP and the solution.
> Everything seems fine (I’ve checked both A and q with MatView and VecView) but I’m having problems getting the solution in a “normal” local double precision fortran vector.
> 
> To be more than sure I’ve tried to repeat the necessary steps in order to achieve this result on qvec :
> 
> After creating and calling a VecScatter in order to bring a sequential version on all the processors (as described in 
> http://www.mcs.anl.gov/petsc/petsc-as/documentation/faq.html#mpi-vec-to-mpi-vec)
> I’ve tried to use VecGetValue as described in the User manual in the Fortran users chapter (pag. 147-148)
> It seems to fail in both the local xx_v vector (that has wrong values) and in calculating the i_x index offset that has a very large negative value
> that, when it is used, generates an obvious “Aut of bound” error.

   It is completely possible that i_x is a very large negative value, in fact it usually is.

   From the users manual:  Note: If using VecGetArray(), MatDenseGetArray(), or ISGetIndices(), from Fortran, the user must not compile the Fortran code with options to check for “array entries out of bounds” (e.g., on the IBM RS/6000 this is done with the -C compiler option, so never use the -C option with this).

  My guess is that your Fortran compiler is checking for array out of bounds and (of course) finding them since xx_v() is declared as xx_v(1). You need to turn of this array bounds checking when compiling. Or you can use VecGetArrayF90().

   Barry



> I’ve tried to use VecGetValue also on qvec directly : same result!
> 
> There must be something wrong that I’m doing.
> Can anybody point me in the right direction?
> Thanks 
> 
> Regards
> Valerio Grazioso
> 
> 
> Here it is the relevant code:
> 
> 
> 
> #define xx_a(ib)  xx_v(i_x + (ib))
> 
> …………………..  
> 
>      Vec         xSEQ
>      PetscScalar xx_v(1)
>      PetscOffset i_x
> 
>      ……………………..
>     ………………..
> 
> 
>      write(6,'(a,i2,a)'),"Processor  ",mpi_rank,": petsc_solve ---> VecCreate"
>      call VecCreate(comm,qvec,ierr); CHKERRQ(ierr)     
> 
>      write(6,'(a,i2,a)'),"Processor  ",mpi_rank,": petsc_solve ---> VecSetSizes"
>      call VecSetSizes(qvec,PETSC_DECIDE,NCELL,ierr); CHKERRQ(ierr)
> 
>      write(6,'(a,i2,a)'),"Processor  ",mpi_rank,": petsc_solve ---> VecSetFromOptions"
>      call VecSetFromOptions(qvec,ierr); CHKERRQ(ierr)
> 
>      write(6,'(a,i2,a)'),"Processor  ",mpi_rank,": petsc_solve ---> VecDuplicate"
>      call VecDuplicate(qvec,xvec,ierr); CHKERRQ(ierr)
> 
>      write(6,'(a,i2,a)'),"Processor  ",mpi_rank,": petsc_solve ---> VecGetOwnershipRange"
>      call VecGetOwnershipRange(qvec,Istart,Iend,ierr); CHKERRQ(ierr)
> 
>      write(6,'(a,i2,a,2i8)'),"Processor  ",mpi_rank,": petsc_solve ---> Istart,Iend (Vet)=", Istart,Iend
> 
>      do Iproc = 0,(mpi_size-1)
>        if (Iproc == mpi_rank) then 
>          do I= (Istart+1), (Iend)
> C            write(6,'(a,i2,a,2i8)'),"Processor  ",mpi_rank,": petsc_solve ---> MatSetValues",I,I
>            call VecSetValues(qvec,1,I-1,SU(I),INSERT_VALUES,ierr); CHKERRQ(ierr)
>            call VecSetValues(xvec,1,I-1,0.E0,INSERT_VALUES,ierr); CHKERRQ(ierr)
>          enddo
>        endif
>      enddo
> 
>      write(6,'(a,i2,a)'),"Processor  ",mpi_rank,": petsc_solve ---> VecAssemblyBegin"
>      call VecAssemblyBegin(qvec,ierr); CHKERRQ(ierr)
>      call VecAssemblyEnd(qvec,ierr); CHKERRQ(ierr) 
>      call VecAssemblyBegin(xvec,ierr); CHKERRQ(ierr) 
>      call VecAssemblyEnd(xvec,ierr); CHKERRQ(ierr) 
>      write(6,'(a,i2,a)'),"Processor  ",mpi_rank,": petsc_solve ---> VecAssemblyEnd"
> 
> C ---------------------------------  DEBUG -------------------------------------
>      if (1 == 1) then
> 
>         call VecScatterCreateToAll(qvec,ctx,xSEQ,ierr); CHKERRQ(ierr)
>         call VecScatterBegin(ctx,qvec,xSEQ,INSERT_VALUES,SCATTER_FORWARD,ierr)
>         CHKERRQ(ierr)
>         call VecScatterEnd(ctx,qvec,xSEQ,INSERT_VALUES,SCATTER_FORWARD,ierr)
>         CHKERRQ(ierr)
>         call VecScatterDestroy(ctx,ierr); CHKERRQ(ierr)
> 
> C         call PetscViewerCreate(comm, view, ierr); CHKERRQ(ierr)
> C         call PetscViewerSetType(view, PETSCVIEWERASCII, ierr); CHKERRQ(ierr)
> C         call PetscViewerSetFormat(view, PETSC_VIEWER_ASCII_INDEX, ierr)
> C         CHKERRQ(ierr)
> C         call PetscViewerFileSetName(view, 'qvec.m', ierr)
> C         call VecView(xSEQ, view, ierr); CHKERRQ(ierr)
> C         call PetscViewerDestroy(view, ierr); CHKERRQ(ierr)
> 
>         call VecGetArray(xSEQ,xx_v,i_x,ierr); CHKERRQ(ierr)
> 
>            write(6, *) (xx_a(I), I=1,NCELL)
>            write(6,'(a,i20)')"i_x = ", i_x 
> 
> 
>         call VecRestoreArray(xSEQ,xx_v,i_x,ierr); CHKERRQ(ierr)
> 
>         call PetscFinalize(ierr); CHKERRQ(ierr)
>         STOP
>      endif
> C ---------------------------------- END DEBUG ------------------------------
> 
>