<div dir="ltr"><div class="gmail_quote">On Thu, Apr 7, 2011 at 15:49, Ryan Yan <span dir="ltr"><<a href="mailto:vyan2000@gmail.com">vyan2000@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 id=":6gg">I agree that solves are faster than factorization and GMRES <br>use more MatVecMult, even with exact preconditioner. So I guess<br>PREONLY is meaning direct solve without forming any sub-space and just<br>
one forward and backward substitutions?</div></blockquote></div><br><div>Yes. Because of the way GMRES works with zero initial guess, there will be two MatSolve and one MatMult even when using a direct solver. PREONLY does one MatSolve and zero MatMult.</div>
</div>