Hello I am trying to speed up a linear elasticity problem with isotropic and heterogeneous properties. It is a topology optimization problem, therefore some regions have an almost zero stiffness whereas other regions have a higher value, making the matrix ill-conditioned. So far, from having searched mail lists on similar problems, I have come up with the following CL options to pass to the petsc solver (two dimensional problem):
-ksp_type cg -pc_type fieldsplit -pc_fieldsplit_block_size 2 -fieldsplit_pc_type hypre -fieldsplit_pc_hypre_type boomeramg -fieldsplit_pc_hypre_boomeramg_strong_threshold 0.7 -pc_fieldsplit_0 0,1 -pc_fieldsplit_type symmetric_multiplicative -ksp_atol 1e-10 It works reasonably well and shows similar number of iterations for different levels of refinement. However, it does not converge at all for the adjoint_solve(), giving the reason DIVERGED_INDEFINITE_PC. I changed the call to KSPSolveTranspose() to KSPSolve() in the file petsc_linear solver.C and that makes the adjoint_solve() converge with the same or better convergence than the forward solve() and I obtain the same sensitivities because the matrix is symmetric. What could I change in my CL options to avoid the DIVERGED_INDEFINITE_PC? Related to this issue, I would like to pass the rigid body modes to a multigrid preconditioner. I’ve seen that there is an interface in libMesh through PetscNonlinearSolver::nearnullspace, but my system is a FEMSystem with a NewtonSolver. It looks like it is not related to the PetscNonlinearSolver. Is there anyway to do this with FEMSystem? Is there any example that uses PetscNonlinearSolver::nearnullspace calculating that nearnullspace? Thanks, Miguel A. Salazar de Troya Graduate Scholar, Lawrence Livermore National Laboratory Ph.D. Candidate, University of Illinois at Urbana-Champaign T1878 Rm: 112 Ext: 2-6411 L-code: 288 ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ Libmesh-users mailing list Libmesh-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libmesh-users
