extremly slow MatSetValues

[Matthew Knepley]

Your matrix is not correctly preallocated:

http://www.mcs.anl.gov/petsc/petsc-as/documentation/faq.html#slow

  Matt

On Sun, Sep 20, 2009 at 10:44 AM, Pierre-Yves Aquilanti <sperif at gmail.com>wrote:

> Hello,
>
> i'm facing a very slow MatSetValues during the discretization of my
> mathematical problem when creating the matrix.
> My matrix is seven banded, come from the a discretization of an helmholtz
> problem using finite differences.
>
> In the 2D case, creating the matrix is really fast. But in 3D case it goes
> well for the first second loop processing and then it goes really really
> slow. Here is a small part of my code :
>
>
> ierr = DAGetCorners(*da, &Istartx, &Istarty, &Istartz, &Iendx, &Iendy,
> &Iendz);
>    CHKERRQ(ierr);
>
>        for (j = Istartz; j < Istartz + Iendz; j++) {
>
>            for(k=Istarty; k < Istarty+Iendy; k++){
>                for (i = Istartx; i < Istartx + Iendx; i++) {
>
>
>                /*get values on an array, their coordinate too*/
>
>
>  MatSetValues(*B,1,ind_mat_x,value_count,ind_mat_y,val_mat_ligne,ADD_VALUES);
>        }
> }
>
> Did you encounter any slowness for MatSetValues function ?
>
> Thanks a lot
>
> Regards
>
>
> PYA
>



-- 
What most experimenters take for granted before they begin their experiments
is infinitely more interesting than any results to which their experiments
lead.
-- Norbert Wiener
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