On Wed, Sep 24, 2008 at 11:21 AM, Etienne PERCHAT <etienne.perchat at transvalor.com> wrote: > Dear Petsc users, > > > > I come again with my comparisons between v2.3.0 and v2.3.3p8. > > > > I face a non repeatability issue with v2.3.3 that I didn't have with v2.3.0. > > I have read the exchanges made in March on a related subject but in my case > it is at the first linear system solution that two successive runs differ. > > > > > > It happens when the number of processors used is greater than 2, even on a > standard PC. > > I am solving MPIBAIJ symmetric systems with the Conjugate Residual method > preconditioned ILU(1) and Block Jacobi between subdomains. > > This system is the results of a FE assembly on an unstructured mesh. > > > > I made all the runs using -log_summary and -ksp_truemonitor. > > > > Starting with the same initial matrix and RHS, each run using 2.3.3p8 > provides slightly different results while we obtain exactly the same > solution with v2.3.0. > > > > With Petsc 2.3.3p8: > > > > Run1: Iteration= 68 residual= 3.19515221e+000 tolerance= > 5.13305158e+000 0 > > Run2: Iteration= 68 residual= 3.19588481e+000 tolerance= > 5.13305158e+000 0 > > Run3: Iteration= 68 residual= 3.19384417e+000 tolerance= > 5.13305158e+000 0 > > > > With Petsc 2.3.0: > > > > Run1: Iteration= 68 residual= 3.19369843e+000 tolerance= > 5.13305158e+000 0 > > Run2: Iteration= 68 residual= 3.19369843e+000 tolerance= > 5.13305158e+000 0 > > > > If I made a 4proc run with a mesh partitioning such that any node could be > located on more than 2 proc. I did not face the problem.
It is not clear whether you have verified that on different runs, the partitioning is exactly the same. Matt > I first thought about a MPI problem related to the order in which messages > are received and then summed. > > But it would have been exactly the same with 2.3.0 ? > > > > Any tips/ideas ? > > > > Thanks by advance. > > Best regards, > > > > Etienne Perchat -- 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
