On Wed, Aug 27, 2014 at 3:54 PM, Xiangdong <[email protected]> wrote:
> Hello everyone, > > When I ran the same petsc codes on different clusters many times, one > cluster always produces the same results, while the other one varies in > terms of number of iterations for SNES and KSP convergence. If the problem > is ill-conditioned, the round-off errors may cause different number of > iterations to converge. However, what puzzles me is that the number of > iterations on one machine is always the same while the other varies. I use > same codes with same version of PETSc. The differences I can think about > are MPI implementations (mvapich2 vs openmpi), compiler (icc vs gcc) and > the network between the nodes. Could these factors cause these different > behaviors? > Some machines (like BlueGene) have very consistent behavior, including the ordering of communication operations, whereas other machines do not. For ill-conditioned problems, this can make a real difference. However, what this is telling you is that your answer is not really any more meaningful than that spread. Matt > Thank you. > > Best, > Xiangdong > -- 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
