<div class="gmail_quote">On Wed, May 9, 2012 at 3:57 PM, Mårten Ullberg <span dir="ltr"><<a href="mailto:martenullberg@gmail.com" target="_blank">martenullberg@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=":42q">it is actually a steady-state solution I'm looking for. Didn't think<br>
it would be that hard. I'll let you know if find any appropriate<br>
method to go with my problem.<br></div></blockquote><div><br></div><div>The indefinite Helmholtz problem is notoriously difficult at high frequency. </div><div><br></div><div><a href="http://www.mathe.tu-freiberg.de/~ernst/PubArchive/helmholtzDurham.pdf">http://www.mathe.tu-freiberg.de/~ernst/PubArchive/helmholtzDurham.pdf</a></div>
<div><br></div><div>For low frequency, many standard methods will work.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div id=":42q">
<br>
One other question, is it big difference between the symmetric QMR<br>
method from the two other QMR methods implemented in PETSc? I've found<br>
some references too that method and indefinite problems.</div></blockquote></div><br><div>Just try it. The QMR algorithms are not equivalent, but they have worked similarly for some other people solving indefinite problems. If you don't have an imaginary shift, it would be standard to use MINRES.</div>