Hugo Gagnon <opensource.petsc at user.fastmail.fm> writes: > Linear elasticity,
Smoothed aggregation is a good choice. > which yields symmetric positive definite matrices. Note that ILU can produce negative pivots for SPD matrices. See Kershaw 1978 or src/ksp/pc/examples/tutorials/ex1.c for a 4x4 example. > So I guess I could reformulate my question to: what is the > solver/preconditioner combination that is "best" suited for this kind > of problem? I tried Anton suggestion and gave BCGS a shot but > although it does seem to work it converges very slowly. Using the > gamg preconditioner blows up: What do you mean "blows up"? Does this problem have sufficient boundary conditions to be non-singular? For elasticity, you should set the "near null space" (rigid body modes) using MatSetNearNullSpace (and perhaps MatNullSpaceCreateRigidBody). Once this is set, you can compare PCGAMG to PCML.
