<div class="gmail_quote">On Sun, Jan 23, 2011 at 03:39, Gaurish Telang <span dir="ltr"><<a href="mailto:gaurish108@gmail.com">gaurish108@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=":2ug">But for this I had to compute U(transpose)U explicitly. The algorithm mentioned in the paper does NOT involve an explicit computation of U(transpose)U. <br>
<br>Is there a way to avoid the explicit and expensive computation of U(transpose)U and use KSPLSQR? The details on this page </div></blockquote></div><br><div>The need for explicit U^T U is for algebraic preconditioners (like incomplete factorization). You can try using cheaper approximations to this product or use a PCShell if you want to avoid explicitly forming the product. Chances are that unpreconditioned LSQR will converge too slowly.</div>