Re: Performance issue with MatSetValues

["Matthew Knepley" <knepley@xxxxxxxxx>]

It sounds like you are inserting values which were not preallocating. To
determine for sure, we would need to know more about the code. However,
if you have a periodic problem, why not use a periodic DA?

  Matt

On 8/10/06, Christophe Picard <picard2@xxxxxxxx> wrote:
> Hi,
>
> I have a performance issue while trying to insert values in the a matrix. I am
> using DMMG solver for cell-centered scheme in 3D from the petsc-snapshot to
> solve a Poisson equations. Inserting coefficients in the matrix for dirichlet
> or neumann boundary conditions, the insertion is instantaneous. But is I want
> to insert coefficients for periodic boundary conditions, I can notice a huge
> slow down in the insertion process (not in the resolution though).
> The smallest size I can notice the performance drop is 32*32*32.
>
> Is there any way to improve this?
>
>
> col.i  = row.i+(mx-1);
> col.j  = row.j;
> col.k = row.k;
>
> v[0] =  1;
>
> MatSetValuesStencil(*A,1,&row,1,&col,v,ADD_VALUES);
>
>
>
> Thans,
>
> Christophe


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