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? Thanks, Dave > For the best results from GAMG you need to give it null space information > but we can worry about that later. > > Mark
