<div class="gmail_quote">On Tue, Oct 11, 2011 at 10:33, behzad baghapour <span dir="ltr"><<a href="mailto:behzad.baghapour@gmail.com">behzad.baghapour@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
What is the difference between "unpreconditioned resid norm" </blockquote><div><br></div><div>This is estimated implicitly using the Krylov iteration. It can become inaccurate if the Krylov basis loses orthogonality (an issue of numerical stability).</div>
<div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">and "true resid norm" in -ksp_monitor?</blockquote></div><br><div>This builds the residual explicitly. It is expensive with some methods, e.g. GMRES.</div>