Thank you very much for this preprint, Lawrence. I have also planned to use the pressure mass matrix for the A11 block.
Unfortunately, at this time, I have no time for implementing things. What I would like to do is to get the best out of the built-in methods of fieldsplit/PETSc. Any hint is welcome! Nicolas 2016-12-13 19:02 GMT+01:00 Lawrence Mitchell < [email protected]>: > > > 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 > >
