[petsc-users] Passing array of PETSc Vec's to a function and returning it

[Jose E. Roman]

Probably you are requesting more eigenvectors than actually computed. Argument i should be smaller than nconv, see https://slepc.upv.es/documentation/current/docs/manualpages/EPS/EPSGetEigenvector.html
Jose


> El 22 jul 2020, a las 10:25, rmondaini at csrc.ac.cn escribió:
> 
> I am trying to pass an array of Vec's in PETSc to a function, modify it internally and retrieve the results. The idea is to copy a handful of eigenvectors from the EPS solver to the main routine. A pseudocode is as follows:
> 
> #include <slepceps.h>
> 
>     PetscErrorCode foo(Vec **y, int n) {
> 
>         EPS            eps;         // eigenproblem solver context
> 
>        // ...
> 
>         ierr = MatCreateVecs(H, &x, NULL); CHKERRQ(ierr);
> 
>         ierr = EPSSolve(eps); CHKERRQ(ierr);
> 
>     // ...
> 
>       ierr = VecDuplicateVecs(x, n, y); CHKERRQ(ierr);
> 
>        for (int i = 0; i < n ; i++) {    // I can guarantee that n < nconv
> 
>            ierr = EPSGetEigenvector(eps, i, *y[i], NULL); CHKERRQ(ierr);   // this breaks for i = 1
> 
>            ierr = VecNorm(*y[i],NORM_2,&norm); CHKERRQ(ierr);   // this prints out fine for i = 0 (norm = 1)
> 
>            printf("norm = %f\n", norm);
> 
>         }
> 
>         ierr = EPSDestroy(&eps); CHKERRQ(ierr);
>         ierr = VecDestroy(&x); CHKERRQ(ierr);
> 
>         return ierr;
> 
>     }
> 
>     int main(int argc,char **argv)
>     {
>         PetscErrorCode ierr;
>         PetscScalar norm;
>         Vec *y;
> 
>         foo(&y, 3);
> 
>         ierr = VecDestroyVecs(3, &y); CHKERRQ(ierr);
> 
>         return 0;
>     }
> 
> Am I making a naive mistake here?
>