[petsc-users] Wrong variable name in MatView with PETSC_VIEWER_ASCII_MATLAB

[Barry Smith]

  Michael,

    Thanks for reporting this. I have fixed it in out maint and master branch and it will be fixed in our next patch update. I've also attached a patch file that you can use to update your copy of PETSc.  
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Note 1:  The reason for the zzz = zeros(3,3); is that for large matrices in Matlab it is (was?) much better to allocate a array of the correct final size before actually providing the entries in the matrix, otherwise Matlab would slowly dynamically keep increasing the size of the matrix as it found more entries in the matrix you provided. This is why we have this line.

zzz = zeros(3,3);
zzz = [
1 1  1.0000000000000000e+00
2 2  1.0000000000000000e+00
3 3  1.0000000000000000e+00
];
 A = spconvert(zzz);

Note: 2 If the matrix is large at all you do not want to save as an ASII matlab file. Instead save using the binary viewer and use the PETSc Matlab script PetscBinaryRead() to read it into Matlab. This will be much much faster for large matrices. For tiny matrices using the ASCII viewer is fine.

   Thanks
   Barry

   

> On Jan 17, 2015, at 2:29 PM, Michael Souza <souza.michael at gmail.com> wrote:
> 
> The name of variable created by MatView using PETSC_VIEWER_ASCII_MATLAB is not the expected one. More clearly, the name of variable is "zzz" no matter what you set by calling PetscObjectSetName. 
> 
> The code below reproduces the unexpected behaviour. There, I create a diagonal MATMPIAIJ matrix and I set its name to "A", but the name of created variable in MATLAB's script is "zzz".
>  
> I also would like to point that there is no need to print the line "zzz = [m n];" once its value will not be used and it will produce an warning at Matlab's editor. So I think it could be removed.
> 
> Note: This strange behaviour doesn't occur with MATSEQAIJ matrices.
> 
> Cheers,
> Michael Souza
> ----------------------------------------------------------
> int main(int argc, char **args) {
>     PetscErrorCode ierr;
>     Mat A;
>     PetscInt i, N = 3;
> 
>     ierr = PetscInitialize(&argc, &args, (char *) 0, help);CHKERRQ(ierr);
> 
>     // matrix creation and setup
>     ierr = MatCreate(PETSC_COMM_WORLD, &A);CHKERRQ(ierr);
>     ierr = MatSetType(A, MATMPIAIJ);CHKERRQ(ierr);
>     ierr = MatSetSizes(A, PETSC_DECIDE, PETSC_DECIDE, N, N);CHKERRQ(ierr);
>     ierr = MatSetUp(A);CHKERRQ(ierr);
>     for (i = 0; i < N; i++) {
>         ierr = MatSetValue(A, i, i, 1.0, INSERT_VALUES);CHKERRQ(ierr);
>     }
>     ierr = MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
>     ierr = MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
> 
>     // matlab viewer
>     ierr = PetscViewerSetFormat(PETSC_VIEWER_STDOUT_WORLD, PETSC_VIEWER_ASCII_MATLAB);CHKERRQ(ierr);
>     ierr = PetscObjectSetName((PetscObject) A, "A");CHKERRQ(ierr);
>     ierr = MatView(A, PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
> 
>     // free memory
>     ierr = MatDestroy(&A);CHKERRQ(ierr);
> 
>     ierr = PetscFinalize();CHKERRQ(ierr);
> 
>     return EXIT_SUCCESSSS;
> }
> ----------------------------------------------------------
>