This sounds like the stopping criteria are different. Matt
On Jan 25, 2008 5:28 PM, USUARIO INICIAL <ronanrmo at ig.com.br> wrote: > I have a conjugate gradient implemented in C without Petsc and when I > solve the linear system of my problem (an elliptic pde) it converges > with something about 270 iterations. But with Petsc (ksp_type cg > pc_type none) the same linear system converges with 510 iterations. > > Do someone have any idea why is that happenning? > > I already checked the matrix and they are equal. The results are quite > close and I set the same tolerance to both methods (setting rtol on > petsc to a very small number, to use only atol). And besides the > number of iterations, the time spent by petsc is not much more than > the other method. > > Thanks, > Ronan > > I'm sorry, I dont know english very well, I did the best I could. > > -- 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
