[petsc-users] setting a vector with VecSetValue versus VecSetValues

[Junchao Zhang]

VecSetValue() also needs global indices, so you need PetscInt gl_row = (
PetscInt)(i)+rstart;

--Junchao Zhang


On Thu, Jan 5, 2023 at 11:25 AM Alfredo Jaramillo <ajaramillopalma at gmail.com>
wrote:

> dear PETSc developers,
>
> I have a code where I copy an array to a distributed petsc vector with the
> next lines:
>
> 1 for (int i = 0; i < ndof_local; i++) {
> 2 PetscInt gl_row = (PetscInt)(i)+rstart;
> 3 PetscScalar val = (PetscScalar)u[i];
> 4 VecSetValues(x,1,&gl_row,&val,INSERT_VALUES);
> 5 }
>
> // for (int i = 0; i < ndof_local; i++) {
> // PetscInt gl_row = (PetscInt)(i);
> // PetscScalar val = (PetscScalar)u[i];
> // VecSetValue(x,gl_row,val,INSERT_VALUES);
> // }
>
> VecAssemblyBegin(x);
> VecAssemblyEnd(x);
>
> This works as expected. If, instead of using lines 1-5, I use the lines
> where VecSetValue is used with local indices, then the vector is null on
> all the processes but rank 0, and the piece of information at rank zero is
> incorrect.
>
> What could I be doing wrong?
>
> bests regards
> Alfredo
>
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