Michele Rosso <[email protected]> writes: > I noticed that the problem appears even if I use CG with the default > preconditioner: commenting KSPSetDM() solves the problem.
Okay, this issue can't show up if you use SNES, but it's a consequence of making geometric multigrid work with a pure KSP interface. You can either use KSPSetComputeOperators() to put your assembly in a function (which will also be called on coarse levels if you use -pc_type mg without Galerkin coarse operators) or you can can provide the Jacobian using KSPSetOperators() as usual, but also call KSPSetDMActive() so that the DM is not used for computing/updating the Jacobian. The logic is cleaner in petsc-3.4 and I think it just does the right thing in your case. > So basically without a proper grid (it seems no grid with an even > numbers of nodes qualifies) and with my own system matrix, I cannot use > any type of multigrid > pre-conditioner? You can use all the AMG methods without setting a DM.
