<html><head><meta http-equiv="Content-Type" content="text/html charset=iso-8859-1"><base href="x-msg://2490/"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>I assume this is a Lapacian and its not a pure Neumann problem. I did not quite follow you description. Do you have some Dirichlet BCs?</div><div><br></div><div>Hypre is a very robust solver, for a scalable solver. ILU, the default PC, is very robust but slow (that's why its the default). You could try gamg, another AMG solver to get another data point.</div><br><div><div>On Oct 7, 2013, at 3:08 PM, Roc Wang <<a href="mailto:pengxwang@hotmail.com">pengxwang@hotmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div class="hmmessage" style="font-size: 12pt; font-family: Calibri; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div dir="ltr">Hello,<br><br> I am trying to solve a linear system with KSP for a 3-D domain. The computational domain is a cubic space with Neumann condition on the lateral sides( y, and z directions). A smaller round plate is on the left side in x direction. The right side is a rectangular plane either with or without a hole. In testing studies, the KSP solver works fine both with and without -pc_type hypre runtime option for the domain with a whole plane(without a hole) on the right, but diverges for the case of a plane with a hole with -ps_type hypre option.<span class="Apple-converted-space"> </span><br><br> My question is whether the hypre pre-conditioner is sensitive to the geometry boundary? If the answer is yes, is there any other pre-conditioner available for my particular case(the domain with a plane which with a hole on the right side) to reduce the number of iterations? Thanks in advance.<br></div></div></blockquote></div><br></body></html>