On Tue 2008-11-11 13:05, mspieg wrote: > On a related thread, > I think there is a bug in the Newton solvers (in 0.8.1) in that they now > don't zero the correction dx before each linear solve. For direct solvers > this isn't a problem, however for krylov methods (in particular > PETScKrylovSolver), this ends up passing the last correction as the initial > guess for the next iteration. Eventually, when the residual becomes > sufficiently small, this throws a divergence_tolerance error in Petsc. (To see > this, just change the solver in demo/nls/nonlinearpoisson to something like > gmres/ilu and use Petsc as the back end).
This is absolutely correct. I didn't understand Garth's comment earlier in this thread > > It's also useful for Newton solvers. How would you obtain a guess of the next Newton correction? Jed
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