[petsc-users] How to get values from a matrix and set again?

[Bibrak Qamar]

Thanks

Bibrak Qamar


On Mon, Dec 7, 2015 at 2:17 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   Presumably you are using a MPIAIJ matrix. You can use
>
>   Mat x,A,B;
>   MatMPIAIJGetSeqAIJ(x,&A,&B,NULL);
>
>   PetscScalar *a;
>   MatSeqAIJGetArray(A,&a);
>   MatInfo info;
>   MatGetInfo(A,MAT_LOCAL,&info);
>   for (i=0; i<info.nz_used; i++) {
>      a[i] = yourfunction(a[i])
>   }
>   MatSeqAIJRestoreArray(A,&a);
>   /* do same thing for B matrix */
>
> > On Dec 7, 2015, at 12:11 AM, Bibrak Qamar <bibrakc at gmail.com> wrote:
> >
> > Hi,
> >
> > I am trying to apply a function on each element of a matrix. The
> function is the sigmoid function which transforms each element of the
> matrix.
> >
> > I am trying to approach it like this but get error. What could be the
> problem? Or is there a better way to do this?
> >
> > int sigmoid(Mat x){
> > printf("in sigmoid\n");
> >
> > PetscErrorCode ierr;
> > PetscInt       Istart, Iend, Ii, Ji, rows, cols;
> >
> > PetscScalar     v = 0.0;
> > ierr = MatGetOwnershipRange(x,&Istart,&Iend);CHKERRQ(ierr);
> > MatGetSize(x,&rows,&cols);
> >
> > for (Ii=Istart; Ii<Iend; Ii++) {
> >      for (Ji=0; Ji<cols; Ji++){
> >     ierr = MatGetValues(x,1,&Ii,1,&Ji,&v);CHKERRQ(ierr);
> >     v = mysigmoid(v);
> >     ierr = MatSetValues(x,1,&Ii,1,&Ji,&v,INSERT_VALUES);CHKERRQ(ierr);
> >     }
> >   }
> >
> > MatAssemblyBegin(x,MAT_FINAL_ASSEMBLY);
> > MatAssemblyEnd(x,MAT_FINAL_ASSEMBLY);
> >
> >
> > MatView(x,PETSC_VIEWER_STDOUT_WORLD);
> > }
> >
> >
> > error msg is:
> >
> > [0]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> > [0]PETSC ERROR: Object is in wrong state
> > [0]PETSC ERROR: Not for unassembled matrix
> > [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
> > [0]PETSC ERROR: Petsc Release Version 3.6.3, Dec, 03, 2015
> > [
> > [0]PETSC ERROR: #1 MatGetValues() line 1780 in
> /gpfs/home/petsc-3.6.3/src/mat/interface/matrix.c
> > [0]PETSC ERROR: #2 sigmoid() line 21 in neural.c
> >
> >
> > Thanks
> > Bibrak Qamar
> >
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20151208/2d94aaec/attachment.html>