<div class="gmail_quote">On Mon, May 9, 2011 at 19:06, Danesh Daroui <span dir="ltr"><<a href="mailto:danesh.daroui@ltu.se">danesh.daroui@ltu.se</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div id=":4xf">Thanks for the tip, but I already have two different version of my<br>
solver with PARDISO and MUMPS. Sparse Direct Solvers gave us a great<br>
contribution but I need to move to O(n^2) time complexity, So I really<br>
need to employ iterative solvers! :)</div></blockquote></div><br><div>I'm confused. Is your problem dense? If so, then it doesn't make sense to use sparse solvers. If it is sparse, then the asymptotics for a direct solver are O(n^{3/2}) flops and O(n log n) space in two dimensions and O(n^2) flops and O(n^{4/3}) spare in three dimensions.</div>
<div><br></div><div>You can still use PETSc, but sparse preconditioners won't help you. In particular, ILU is just a really crappy direct solver if you use it on a dense matrix. Are there preconditioners for your problem in the literature? Can it be done with a hierarchical method like FMM?</div>