Ok, thank you for pointing me to this paper. On 21.03.2012 11:38, Jed Brown wrote: > On Wed, Mar 21, 2012 at 04:03, Alexander Grayver > <agrayver at gfz-potsdam.de <mailto:agrayver at gfz-potsdam.de>> wrote: > > Hello, > > Plotting values of relative residual norm versus iteration I > noticed that these curves have different behavior. For instance, > ones I got with BiCGStab are oscillatory and rather noisy with > large jumps within few iterations. Curves for QMR are smooth, > however it's usual that they stagnate for ~10-20 iterations and > then go down further. Same preconditioner is applied for both and > both methods are Lanczos based, so I don't understand this. > I'm wondering is this just my specific case or there is general > explanation for that? > > > This is normal. > > http://people.maths.ox.ac.uk/trefethen/publication/PDF/1992_52.pdf
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