<div>Thank you guys, </div>What happens right now when I use GMRES is that it reaches the maximum number of iterations I set, i.e. 1000 (which should not). I have set the restart to 20 (and then increased it to 1000) but no luck. It never converges. <div>
<br><div><br><div class="gmail_quote">On Fri, Dec 23, 2011 at 7:23 AM, Jed Brown <span dir="ltr"><<a href="mailto:jedbrown@mcs.anl.gov">jedbrown@mcs.anl.gov</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="im"><div class="gmail_quote">On Fri, Dec 23, 2011 at 07:43, Matthew Knepley <span dir="ltr"><<a href="mailto:knepley@gmail.com" target="_blank">knepley@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>Even if you lose orthogonality, it will just stagnate since you always have the solution<div>from the first few vectors. Likewise, I do not see how you can get an diverging sequence</div><div>from restarting since you always have the last residual, you just stagnate.</div>
</div></blockquote></div><br></div><div>The true residual can grow even though the estimate of the preconditioned residual decreases monotonically. When you restart, you re-evaluate the actual residual, which might be much larger.</div>
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