Michele Rosso <[email protected]> writes: > Hi, > > I am solving an inhomogeneous Laplacian in 3D (basically a slightly > modified version of example ex34). > The laplacian is discretized by using a cell-center finite difference > 7-point stencil with periodic BCs. > I am solving a time-dependent problem so the solution of the laplacian > is repeated at each time step with a different matrix (always SPD > though) and rhs. Also, the laplacian features large magnitude variations > in the coefficients. I solve by means of CG + GAMG as preconditioner. > Everything works fine for a while until I receive a > DIVERGED_INDEFINITE_PC message.
What is changing as you time step? Is there a nonlinearity that activates suddenly? Especially a bifurcation or perhaps a source term that is incompatible with the boundary conditions? You could try -mg_levels_ksp_type richardson -mg_levels_pc_type sor. Can you reproduce with a small problem? The configuration looks okay to me. > Before checking my model is incorrect I would like to rule out the > possibility of improper use of the linear solver. I attached the full > output of a serial run with -log-summary -ksp_view > -ksp_converged_reason ksp_monitor_true_residual. I would appreciate if > you could help me in locating the issue.
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