On Thu, May 2, 2013 at 9:01 AM, Nico Schl?mer <nico.schloemer at gmail.com>wrote:
> Hi all, > > I'm trying to solve a discretization of the PDE in weak form > > rho/tau u - mu \Delta u = f > > where u is vector-valued (let's say in 2D -- this comes from a > Navier--Stokes problem). Some Dirichlet-boundary conditions come with it, > too. > > After translation in weak form, > > rho/tau * inner(u, v) + mu * inner(grad(u), grad(v)) = inner(f, v) > > I'm solving this with PETSc's CG and hypre_amg. What I get is > > 0 KSP preconditioned resid norm 4.962223194957e+30 true resid norm > 2.364095175749e-02 ||r(i)||/||b|| 1.000000000000e+00 > 1 KSP preconditioned resid norm 7.089043065444e+19 true resid norm > 2.289113027906e-02 ||r(i)||/||b|| 9.682829402926e-01 > > Without preconditioning, I'm getting > > 0 KSP preconditioned resid norm 2.364095175749e-02 true resid norm > 2.364095175749e-02 ||r(i)||/||b|| 1.000000000000e+00 > 1 KSP preconditioned resid norm 4.415430823612e-02 true resid norm > 4.415430823612e-02 ||r(i)||/||b|| 1.867704341562e+00 > 2 KSP preconditioned resid norm 1.077641425707e-01 true resid norm > 1.077641425707e-01 ||r(i)||/||b|| 4.558367348159e+00 > > and DIVERGED_INDEFINITE_MAT. > > Does anyone else have experience with this sort of problems? Any obvious > mistakes? > Do you have any non-symmetries in your discretization? With the standard P_1 basis, that operator is symmetric. Matt > --Nico > > > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130502/9d465dff/attachment.html>
