Roy Stogner <royst...@ices.utexas.edu> writes: > By "neither seems to do much"? > > I mean that if I set either "-ksp_pc_side right" or "-ksp_norm_type > unpreconditioned", then instead of ending up falsely "converged" at > 10 KSP preconditioned resid norm 1.580464771307e-13 true resid norm > 3.084021824157e-04 ||r(i)||/||b|| 2.711608086867e-03 > I end up at > 10 KSP unpreconditioned resid norm 4.683505266751e-14 true resid norm > 3.820485023471e-04 ||r(i)||/||b|| 3.359139032108e-03
Interesting. Can you include the full unpreconditioned output? And please compare with and without -ksp_gmres_modifiedgramschmidt. >>> It's odd that incomplete LU would be singular but incomplete Cholesky >>> would work fine, too, isn't it? >> >> Where do you see ILU being singular while ICC is not? > > Right here, assuming the singular preconditioner theory is correct. > With the default (or with explicitly set) "-pc_type ilu" I see the > above; with "-pc_type icc" I end up at > 92 KSP preconditioned resid norm 1.322044991650e-13 true resid norm > 8.345374951602e-14 ||r(i)||/||b|| 7.337621942051e-13 > or > 93 KSP unpreconditioned resid norm 6.339459949689e-14 true resid norm > 6.339403586772e-14 ||r(i)||/||b|| 5.573883393805e-13 > depending on whether I set "-ksp_norm_type unpreconditioneed" > >> What do you intend ICC to mean if the matrix is nonsymmetric? > > Mu. The matrix is symmetric. Loading it up in Octave I get > norm(K)=2.0000, norm(K-K')=1.1395e-16 How big is this matrix? Can you write it with "-ksp_view_mat binary" and send it to me (or post somewhere)? >> What KSP are you using here? > > The default (GMRES, IIRC and based on the unchanged results when I set > it explicitly). I briefly tried BCGS when I got the > apparently-mistaken impression from > http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/KSP/KSPSetNormType.html > that -ksp_norm_type wouldn't work with GMRES. Dammit, these lists of methods are always wrong. We give useful error messages if it's not supported. I'll fix/delete these doc problems.
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