On Dec 23, 2011, at 8:36 PM, Dave Nystrom wrote: > Mark F. Adams writes: >> It sounds like you have a symmetric positive definite systems like du/dt - >> div(alpha(x) grad)u. The du/dt term makes the systems easier to solve. >> I'm guessing your hard system does not have this mass term and so is >> purely elliptic. Multigrid is well suited for this type of problem, but >> the vector nature requires some thought. You could use PETSc AMG -pc_type >> gamg but you need to tell it that you have a system of two dof/vertex. >> You can do that with something like: >> >> ierr = MatSetBlockSize( mat, 2 ); CHKERRQ(ierr); > > Best I can tell, the matrix block size cannot be set using a command line > option. It that correct? >
I believe so. Mark > Thanks, > > Dave > >> For the best results from GAMG you need to give it null space information >> but we can worry about that later. >> >> Mark >