> > I'm solving a system with GMRES using the same preconditioner either on > > the left or on the right. > > For left preconditioning I get two orders of reduction for the > > preconditioned residual in 20 its: > > > > Notice here that your "preconditioner" is far from one. It manages to blow > up the true residual by > 5 orders of magnitude, from which it never recovers. The right > preconditioning just avoids being > so screwed up. > > Matt
Yes, I noticed that. It does recover 2 orders in 20 its, and it can recover 5 orders and beyond in a few hundred its. What I don't understand is how the same preconditioner applied to the right "just avoids being so screwed up". Chris dr. ir. Christiaan Klaij CFD Researcher Research & Development E mailto:C.Klaij at marin.nl T +31 317 49 33 44 MARIN 2, Haagsteeg, P.O. Box 28, 6700 AA Wageningen, The Netherlands T +31 317 49 39 11, F +31 317 49 32 45, I www.marin.nl