Hi Jed, Thanks for the reply. I've defined 2 nonzeros per row so it should consider them to be in the correct place (1 for diagonal and 1 for the 1st off diagonal). I do not want to delete anything, just experiment with inserting new entries. This is a simple example to demonstrate my problem with a more complicated code of nonlinear elasticity.
Margarita On 3 February 2012 22:41, Jed Brown <jedbrown at mcs.anl.gov> wrote: > On Sat, Feb 4, 2012 at 01:35, Margarita Satraki < > margarita.satraki at gmail.com> wrote: > >> It seems that only the 1st case gives good results in the sense that by >> increasing the size of the matrix you increase the time needed by >> MatSetValues linearly. Both the 2nd and the 3rd case give similar results, >> much worse than the 1st. I understand that the 1st case has the advantage >> because of accurate memory allocation but shouldn't the 2ndcase be better >> than the 3rd since it at least defines the number of nonzeros per row so it >> again allocates memory more accurately? > > > Those nonzeros are in the wrong place and PETSc does not know that you > want to "delete" the old entries. > > Just preallocate the correct number of nonzeros and it will be fast, don't > bother with copying in a "similar" matrix. > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120203/7a08dddd/attachment.htm>
