On 13/12/16 16:50, Karin&NiKo wrote: > Dear Petsc-gurus, > > I am solving Biot's poroelasticity problem : > Images intégrées 1 > > I am using a mixed P2-P1 finite element discretization. > > I am using the fieldsplit framework to solve the linear systems. Here > are the options I am using : > -pc_type fieldsplit > -pc_field_split_type schur > -fieldsplit_0_pc_type gamg > -fieldsplit_0_pc_gamg_threshold -1.0 > -fieldsplit_0_ksp_type gmres > -fieldsplit_0_ksp_monitor > -fieldsplit_1_pc_type sor > -fieldsplit_1_ksp_type gmres > -pc_fieldsplit_schur_factorization_type upper > > > By increasing the mesh size, I get increasing numbers of outer > iterations. > > According to your own experience, among all the features of > fieldsplit, was is the "best" set of preconditioners for this rather > classical problem in order to get an extensible solver (I would like > to solve this problem on some tens millions of unknowns of some > hundreds of procs)?
Here's a recent preprint that develops a three-field formulation of the problem that gets reasonably mesh and parameter-independent iteration counts using block-diagonal preconditioning. https://arxiv.org/abs/1507.03199 (No need for schur complements) If you can create the relevant blocks it should be implementable with -pc_fieldsplit_type additive Lawrence
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