> On Jan 14, 2016, at 12:57 PM, Jed Brown <[email protected]> wrote: > > Hoang Giang Bui <[email protected]> writes: >> One more question I like to ask, which is more on the performance of the >> solver. That if I have a coupled problem, says the point block is [u_x u_y >> u_z p] in which entries of p block in stiffness matrix is in a much smaller >> scale than u (p~1e-6, u~1e+8), then AMG with hypre in PETSc still scale? > > You should scale the model (as Barry says). But the names of your > variables suggest that the system is a saddle point problem, in which > case there's a good chance AMG won't work at all. For example, > BoomerAMG produces a singular preconditioner in similar contexts, such > that the preconditioned residual drops smoothly while the true residual > stagnates (the equations are not solved at all). So be vary careful if > you think it's "working".
The PCFIEDSPLIT preconditioner is designed for helping to solve saddle point problems. Barry
