<div class="gmail_quote">On Wed, Mar 21, 2012 at 04:03, Alexander Grayver <span dir="ltr"><<a href="mailto:agrayver@gfz-potsdam.de">agrayver@gfz-potsdam.de</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hello,<br>
<br>
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.<br>
I'm wondering is this just my specific case or there is general explanation for that?<br></blockquote><div><br></div><div>This is normal.</div><div><br></div><div><a href="http://people.maths.ox.ac.uk/trefethen/publication/PDF/1992_52.pdf">http://people.maths.ox.ac.uk/trefethen/publication/PDF/1992_52.pdf</a></div>
</div>