"Garth N. Wells" <[email protected]> writes: > On 2014-01-29 12:11, Patrick Farrell wrote: >> On 28/01/14 19:49, Garth N. Wells wrote: >> >>> A plus of this approach is that if your system is symmetric you can >>> use CG or >>> MINRES, which you can't with NonlinearDiscreteProblem. >> >> I don't really understand your comment. Perhaps I've misunderstood. >> You can use >> CG or MINRES perfectly well without subclassing NonlinearProblem >> directly. Try >> it out in the nonlinear-poisson demo. That's using >> NonlinearDiscreteProblem >> under the hood. Am I missing something? >> > > NonlinearDiscreteProblem breaks symmetry when applying bcs.
CG is usually robust to this form of weak asymmetry. MINRES is probably okay since it iterates in a benign space due to the first application of a preconditioner fixing the boundaries. It's still worth implementing symmetric BCs.
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