On Mar 3, 2011, at 6:52 AM, gouarin wrote: > Hi, > > I'm still working on my stokes problem with 2 DM (one for the velocities and > an other for the pressure). I do the best preallocation for my matrix. > After the construction of my matrix, I do a matrix vector operation and I > compare the result for one process and 2 processes. If I pay attention to the > numbering of my fields between these 2 problems, I have the same result. > > But when I do just 2 iterations of my ksp solver, I don't have the same > result at the end and of course the residual is not the same.
What preconditioner are you using? Unless you use Jacobi you will always get a different set of iterations. (And even with Jacobi due to different order of operations you will eventually see a different convergence route between 1 and 2 processes. You cannot be concerned about this, the things to be concerned about are: 1) Do 1 and 2 processes eventually converge to the same answer (bad news if they do not) 2) Does 2 process converge almost as quickly to the answer as one process (bad news if adding more processes slows the convergence greatly so the solution time ends up being longer). Barry > > Do you know what I do wrong ? > > Thanks, > Loic > > -- > Loic Gouarin > Laboratoire de Math?matiques > Universit? Paris-Sud > B?timent 425 > 91405 Orsay Cedex > France > Tel: (+33) 1 69 15 60 14 > Fax: (+33) 1 69 15 67 18 >
