<div class="gmail_quote">On Mon, Nov 21, 2011 at 09:19, Barry Smith <span dir="ltr"><<a href="mailto:bsmith@mcs.anl.gov">bsmith@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 id=":621">Note there is never a reason to use KSP to do the solve because for the many solves needed a direct solver will always win over using an iterative solver</div></blockquote><div><br></div><div>Depends. If multigrid works well on the subdomain problems, then it will definitely win for large subdomains. (Or you might not even be able to afford that amount of memory.)</div>
<div><br></div><div>Yes, you could use smaller subdomains, but most people only write FETI-DP as a 2-level method and the size of the coarse space is a serious problem.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div id=":621"> and since the result is dense it doesn't make sense to do this computation with huge matrices.<br></div></blockquote><div><br></div><div>But you are only solving against a few right hand sides. Between 4 and 200, for example, while the subdomain size might be more than 100k.</div>
<div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div id=":621">
If you want to use an external LU solver (it will not be faster than PETSc's so why bother).</div></blockquote><div><br></div><div>This must be a joke. ;-)</div></div>