Hi, i have a problem for which i am not exaclty sure about what to do. I set up a simple 2D rectangular domain and decompose it into four equal boxes. I then build the petsc matrix based on this layout as well as the corresponsing RHS vector.
I print out the matrix and RHS vector right before my KSPSolve call, and right after that call i print out the solution vector 'x'. I do this for 2 runs. 1) 1 processor 2) 4 processors. For both runs i do a difference (i.e. on the output files using diff) on all 3 quantities (the matrix, the RHS vector and the solution vector). The 'diff' command reports no difference between the files for the matrix and RHS vector. However, the soltution vector is different between the 2 runs. How different depends a little on what precond/solver combination i use and the tolerances. However, for example for BJacobi/GMRES with reltol=abstol=1e-12 the vector element with the maximum difference is on the order 1e-05. This is only after the first timestep. My problem has some nonlinearlity to it such that this will become a problem later on. The worst difference i have seen is if i use hypre's euclid. It was on the order of 1e-02. So my question is whether someone has an idea why this is happening (i suppose it is related to the parallel communication) and if there is way to fix it. thanks matt -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20091007/bc497fa4/attachment.htm>
