<html xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Calibri",sans-serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:#954F72;
text-decoration:underline;}
span.EmailStyle17
{mso-style-type:personal-compose;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style>
</head>
<body lang="EN-US" link="#0563C1" vlink="#954F72">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:11.0pt">Hello,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Up until now, I have been solving my elasticity problem using the gamg preconditioner with the following options:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-ksp_monitor_true_residual <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-ksp_converged_reason<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-ksp_type cg<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-log_view<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-mg_levels_esteig_ksp_type cg<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-mg_levels_ksp_chebyshev_esteig_steps 10<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-mg_levels_ksp_type chebyshev<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-mg_levels_pc_type sor<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-pc_type gamg<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-pc_gamg_verbose 7<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-pc_gamg_type agg<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-pc_gamg_agg_nsmooths 1<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-pc_gamg_threshold 0.001<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-snes_linesearch_type basic<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="ES" style="font-size:11.0pt">-snes_atol 1e-6 <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="ES" style="font-size:11.0pt">-ksp_atol 1e-7 <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-ksp_rtol 1e-9<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-ksp_norm_type unpreconditioned <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">It has worked great so far, even for my problem where I have two materials with more than 1e3 ratio.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Now, when I add robin boundary conditions, the solver fails with DIVERGED_INDEFINITE_PC. Using -ksp_type bcgs makes the solver converge. I imagine it is because it can handle the indefinite PC. Why is the
PC indefinite for the Robin problem? Is there any way to make it positive definite? I am also passing the rigid body modes of my mesh to the solver. I am not sure if these modes change with the Robin boundary conditions, they should not, should they?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Thanks<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Miguel<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Times New Roman",serif">-- <o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</body>
</html>