[petsc-users] save a vector value of multiple DOF to a file

[Li, Zhisong (lizs)]

Hi, Matt,

First let me state the problem again:

I use the following code to write a global solution vector x to a file, which is in 2D domain with multiple DOF (u, v, p) as in a typical CFD problem (like snes/ex19.c):

       VecScatterCreateToZero(x, &scatter, &y);
       VecScatterBegin(scatter, x, y, INSERT_VALUES,SCATTER_FORWARD);
       VecScatterEnd(scatter, x, y, INSERT_VALUES,SCATTER_FORWARD);
       VecScatterDestroy(scatter); 

       DAVecGetArray(da,y,&ww);

       PetscViewerASCIIOpen(PETSC_COMM_WORLD,"./result.txt",&viewer);
       PetscPrintf(PETSC_COMM_WORLD," %G\n ", ww[15][17].p); 

This works correctly for sequential processing. After scattering, I can find both x and y size as 8721 using VecGetSize(). But for parallel processing, DAVecGetArray() produces errors. If I don't use DAVecGetArray(), how can I access the data and write it to a file?

I also tried the following code as you suggested:

       DAGetGlobalVector(da, &x);
       DAVecGetArray(da, x, &ww);

It gives no error for sequential or parallel running, but the value are all 0 (wrong).

I think writing data to a file should be a common utility for PETSc, can you just find me a sample code that I can follow?


Thank you. 


Regards,


Zhisong Li


> >The error message:
>>
> >[1]PETSC ERROR: --------------------- Error Message
> >------------------------------------
> >[1]PETSC ERROR: Arguments are incompatible!
> >[1]PETSC ERROR: Vector local size 0 is not compatible with DA local sizes
> >4284 4437
> >!

>This is your problem. The Vec you pass into DAVecGetArray() does not
>actually come from
>the DA at all, and in fact has size 0. You can get properly sized Vecs using
>DAGetGlobalVector().
>What Vec are you trying to access (since it obviously cannot have valid
>values in it)?

>  Matt