Roy Stogner <royst...@ices.utexas.edu> writes: > Copying discussion from libmesh-users, both because it looks like a > library- rather than a user-level problem and because I'm hoping one > of our PETSc expert lurkers will chime in. > > Summary: running a libMesh adjoint_solve() on a particular coupled > multiphysics system on a small mesh claims to solve the adjoint system > down past 1e-10 tolerance, but manually evaluating the residual > magnitude afterwards shows more like 1e-4. Turning off > preconditioning eliminates the discrepancy.
Can you provide output with -ksp_monitor_true_residual? Are you comparing a preconditioned residual to an unpreconditioned residual? Note that penalty boundary conditions render unpreconditioned residuals nearly useless. > ---------- Forwarded message ---------- > Date: Wed, 7 Jan 2015 17:06:16 -0600 (CST) > From: Roy Stogner <royst...@ices.utexas.edu> > To: libmesh-us...@lists.sourceforge.net > Subject: Re: [Libmesh-users] Adjoint Solve > > > On Wed, 7 Jan 2015, Roy Stogner wrote: > >> Was using PETSc without any good solver packages built in, but >> "-mat_view ::ascii_matlab" and octave were enough to catch the red >> herring; the matrix is fine. > > The matrix is fine, but the preconditioners aren't. If I run with > "-pc_type jacobi" (how does this not NaN with your matrix with zeros > on the diagonal?) or just plain "-pc_type none", then everything's > fine: > > > > ~ *~*~*~*~*~*~*~*~ adjoint solve start ~*~*~*~*~*~*~*~*~ > > number of iterations to solve adjoint: 87 > final residual of adjoint solve: 8.65357e-14 > > ~ *~*~*~*~*~*~*~*~ adjoint solve end ~*~*~*~*~*~*~*~*~ > > ------------ herp derp ------------ > > > adjoint system residual (discrete L2): 8.65326e-14 > adjoint system residual (L2, all): 2.62094e-14 > adjoint system residual (L2, 0): 2.06412e-14 > adjoint system residual (L2, 1): 1.61515e-14 > > > > Are we doing something wrong with the preconditioner code in > PetscLinearSolver::adjoint_solve()? My first thought: maybe the > preconditioner isn't getting transposed properly, so asymmetric > preconditioners like ILU show inconsistent behavior? You've boiled > down the problem to a symmetric matrix, but IIRC ILU application still > won't be symmetric. If we *tell* PETSc to precondition for a > symmetric matrix, with "-pc_type icc", then everything still works > fine... > --- > Roy > > ------------------------------------------------------------------------------ > Dive into the World of Parallel Programming! The Go Parallel Website, > sponsored by Intel and developed in partnership with Slashdot Media, is your > hub for all things parallel software development, from weekly thought > leadership blogs to news, videos, case studies, tutorials and more. Take a > look and join the conversation now. http://goparallel.sourceforge.net > _______________________________________________ > Libmesh-devel mailing list > Libmesh-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/libmesh-devel
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