Michele Rosso <[email protected]> writes: > Jed, > > thanks for your reply. > By using the options you suggested, namely /-mg_levels_ksp_type > richardson -mg_levels_pc_type sor/, I was able to > solve without bumping into the DIVERGED_INDEFINITE_PC message. > Nevertheless, the number of iterations increases drastically as the > simulation progresses.
What about SOR with Chebyshev? (A little weird, but sometimes it's a good choice.) If the solve is expensive, you can add a few more iterations for eigenvalue estimation. > The Poisson's equation I am solving arises from a variable-density > projection method for incompressible multi-phase flows. > At each time step the system matrix coefficients change as a consequence > of the change in location of the heavier phase; the rhs changes > in time because of the change in the velocity field. Usually the > black-box multigrid or the deflated conjugate gradient method are used > to solve efficiently this type of problem: it is my understanding - > please correct me if I am wrong - that AMG is a generalization of the > former. Dendy's "black-box MG" is a semi-geometric method for cell-centered discretizations. AMG is not a superset or subset of those methods. > The only source term acting is gravity; the hydrostatic pressure is > removed from the governing equation in order to accommodate periodic > boundary conditions: this is more a hack than a clean solution. Could it > be the reason behind the poor performances/ DIVERGED_INDEFINITE_PC > problem I am experiencing? If you have periodic boundary conditions, then you also have a pressure null space. Have you removed the null space from the RHS and supplied the null space to the solver?
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