Re: Running squential and parallel linear solver in the same code?

["Ben Tay" <zonexo@xxxxxxxxx>]

Hi Barry,

 

Thanks for your recommendation. I've managed to use mat_view to view the matrix. However, there's something which I don't understand. My linear eqns consist of 36 pts - so I see 36 rows - 0 to 35.

 

For the uniprocessor, I saw 0-35rows. These show the coefficients of my matrix. Then there's a repeat of 0-35 rows again. But what are these values? I don't understand.

 

For the 4 processors, I saw exactly the same 0-35rows. After that I saw 0-8 rows repeated 4 times. The values are now different, even for the same 1st 0 row. Some values are missing. I guess there's where my mistakes are.

 

Thank you.

 

On 1/23/07, Barry Smith <bsmith@xxxxxxxxxxx> wrote:

Ben,

  You can use -pc_type redundant -redundant_pc_type lu to solve the
linear system with a sequential LU to test if that improves the situation.

Likely your generation of the matrix on 2 processes is wrong, you can run
with -mat_view on a small problem with both 1 and 2 processes and see if
they are the same in both cases.

I don't think what you propose to do below makes sense,

  Barry


On Tue, 23 Jan 2007, Ben Tay wrote:

> Hi,
>
> In my MPI CFD code, I have to solve 2 linear eqns - momentum and poisson
> eqn. There's some error in the code and I don't know which one causes the
> error. May I know if it is possible to solve 1 eqn in sequential mode while
> the other in MPI to pinpoint the error since my code works ok in a
> sequential mode.
>
> I tried to use this for one of the eqn:
>
>
> call
> MatCreateSeqAIJ(PETSC_COMM_SELF,size_x*size_y,size_x*size_y,9,PETSC_NULL_INTEGER,A_mat,ierr)
>
> call VecCreateSeq(PETSC_COMM_SELF,size_x*size_y,b_rhs,ierr)
>
> but there's error.
>
> Thank you.
>