Roy Stogner <royst...@ices.utexas.edu> writes: > On Thu, 8 Jan 2015, Jed Brown wrote: > >> Can you provide output with -ksp_monitor_true_residual? Are you >> comparing a preconditioned residual to an unpreconditioned residual? > > Yes, and yes: > > 0 KSP preconditioned resid norm 5.893300515271e-01 true resid norm > 1.137340546775e-01 ||r(i)||/||b|| 1.000000000000e+00 > 1 KSP preconditioned resid norm 1.323095860276e-01 true resid norm > 1.854948903571e-02 ||r(i)||/||b|| 1.630952935627e-01 > 2 KSP preconditioned resid norm 2.957976209084e-03 true resid norm > 9.076848423484e-04 ||r(i)||/||b|| 7.980765698734e-03 > 3 KSP preconditioned resid norm 4.630654713249e-04 true resid norm > 3.394455698647e-04 ||r(i)||/||b|| 2.984555248884e-03 > 4 KSP preconditioned resid norm 1.042927953583e-05 true resid norm > 3.082072165862e-04 ||r(i)||/||b|| 2.709893861255e-03 > 5 KSP preconditioned resid norm 7.161971654746e-07 true resid norm > 3.084038310662e-04 ||r(i)||/||b|| 2.711622582529e-03 > 6 KSP preconditioned resid norm 3.126650757674e-08 true resid norm > 3.084036219553e-04 ||r(i)||/||b|| 2.711620743934e-03 > 7 KSP preconditioned resid norm 1.102895578517e-09 true resid norm > 3.084021853448e-04 ||r(i)||/||b|| 2.711608112620e-03 > 8 KSP preconditioned resid norm 5.540930099957e-11 true resid norm > 3.084021840854e-04 ||r(i)||/||b|| 2.711608101548e-03 > 9 KSP preconditioned resid norm 2.937449992531e-12 true resid norm > 3.084021825944e-04 ||r(i)||/||b|| 2.711608088437e-03 > 10 KSP preconditioned resid norm 1.580464771307e-13 true resid norm > 3.084021824157e-04 ||r(i)||/||b|| 2.711608086867e-03 > number of iterations to solve adjoint: 10 final residual of adjoint solve: > 1.58046e-13
This is usually caused by a singular preconditioner. http://mid.mail-archive.com/87y6iyzl73.fsf@59A2.org > It still seems like we've got to be doing something wrong in > PetscLinearSolver::adjoint_solve(). I haven't tried this myself, but > I'm told that setting up the transpose linearized problem here and > using a straight solve() works fine. What solver configuration is being used? Can you show -ksp_monitor_true_residual output for the original forward solve and the explicitly transposed solve? >> Note that penalty boundary conditions render unpreconditioned residuals >> nearly useless. > > Agreed; fortunately she's using DirichletBoundary constraints. For > this tiny boiled down version of the problem the norm of the matrix is > only 32. > --- > Roy
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