<html xmlns:v="urn:schemas-microsoft-com:vml" 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=us-ascii">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:SimSun;
panose-1:2 1 6 0 3 1 1 1 1 1;}
@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;}
@font-face
{font-family:SimSun;
panose-1:2 1 6 0 3 1 1 1 1 1;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman",serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
span.apple-converted-space
{mso-style-name:apple-converted-space;}
span.EmailStyle18
{mso-style-type:personal;
font-family:"Calibri",sans-serif;
color:#1F497D;}
span.EmailStyle19
{mso-style-type:personal-compose;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:72.0pt 90.0pt 72.0pt 90.0pt;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-SG" link="blue" vlink="purple">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Dear Barry,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Thanks for your explanation. Does it mean the default director solver LU in PETSc can also run in the distributed memory mode? I only used iterative solvers with
preconditioners in distributed memory before. My experience in using director solver in parallel is indeed limited, especially the saddle point problem in parallel. I have done some search online, but I did not find a working set up at this moment. Could
you give a sample setup of the direct solver for parallel run? It is really appreciated.
<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></a></p>
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Barry Smith [mailto:bsmith@petsc.dev]
<br>
<b>Sent:</b> Wednesday, 29 July 2020 9:48 AM<br>
<b>To:</b> Bin Liu <lbllm2018@hotmail.com><br>
<b>Cc:</b> petsc-users@mcs.anl.gov<br>
<b>Subject:</b> Re: [petsc-users] solving saddle point problem in distributed memory<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<p class="MsoNormal"> SuperLU_DIST won't "magically" run on saddle point problems. It only does limited pivoting, realistically a parallel LU cannot always do complete pivoting or it becomes a sequential algorithm. For parallel you need to use PCFIELDSPLIT,
for sequential you can use SuperLU (not SuperLU_DIST) since it can do more pivoting, being a sequential algorithm.<o:p></o:p></p>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal"> Barry<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<p class="MsoNormal"><br>
<br>
<o:p></o:p></p>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<div>
<p class="MsoNormal">On Jul 28, 2020, at 7:59 PM, Bin Liu <<a href="mailto:lbllm2018@hotmail.com">lbllm2018@hotmail.com</a>> wrote:<o:p></o:p></p>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Thanks for your tutorials. Yes. I tried PCFIELDSPLIT. However, it only works for sequential runs. When I run the code in distributed memory, it reports errors.
In fact, the essence of my wonder is (a) how to set up superlu_dist in petsc for solving saddle point problem in distributed memory? (b) does the direct solvers in petsc can run in distributed memory for solving saddle point problem?</span><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> </span><o:p></o:p></p>
</div>
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm">
<div>
<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span class="apple-converted-space"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> </span></span><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">Stefano
Zampini [<a href="mailto:stefano.zampini@gmail.com"><span style="color:purple">mailto:stefano.zampini@gmail.com</span></a>]<span class="apple-converted-space"> </span><br>
<b>Sent:</b><span class="apple-converted-space"> </span>Tuesday, 28 July 2020 6:55 PM<br>
<b>To:</b><span class="apple-converted-space"> </span>Bin Liu <<a href="mailto:lbllm2018@hotmail.com"><span style="color:purple">lbllm2018@hotmail.com</span></a>><br>
<b>Cc:</b><span class="apple-converted-space"> </span><a href="mailto:petsc-users@mcs.anl.gov"><span style="color:purple">petsc-users@mcs.anl.gov</span></a><br>
<b>Subject:</b><span class="apple-converted-space"> </span>Re: [petsc-users] solving saddle point problem in distributed memory</span><o:p></o:p></p>
</div>
</div>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">If you want advice you should post the error trace PETSc reports.<o:p></o:p></p>
</div>
<div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">Anyway, solving Stokes is not so trivial (without direct solvers, you may need mesh dependent information), but we have examples for it<o:p></o:p></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"><a href="https://gitlab.com/petsc/petsc/-/blob/master/src/ksp/ksp/tutorials/ex42.c"><span style="color:purple">https://gitlab.com/petsc/petsc/-/blob/master/src/ksp/ksp/tutorials/ex42.c</span></a><o:p></o:p></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"><a href="https://gitlab.com/petsc/petsc/-/blob/master/src/ksp/ksp/tutorials/ex43.c"><span style="color:purple">https://gitlab.com/petsc/petsc/-/blob/master/src/ksp/ksp/tutorials/ex43.c</span></a><o:p></o:p></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"><a href="https://gitlab.com/petsc/petsc/-/blob/master/src/snes/tutorials/ex69.c"><span style="color:purple">https://gitlab.com/petsc/petsc/-/blob/master/src/snes/tutorials/ex69.c</span></a><o:p></o:p></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal">If you scroll to the end of those files, you see a bunch of possible options either using PCFIELDSPLIT, PCBDDC or KSPFETIDP.<o:p></o:p></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<div>
<p class="MsoNormal"><br>
<br>
<br>
<o:p></o:p></p>
</div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<div>
<div>
<p class="MsoNormal">On Jul 28, 2020, at 12:37 PM, Bin Liu <<a href="mailto:lbllm2018@hotmail.com"><span style="color:purple">lbllm2018@hotmail.com</span></a>> wrote:<o:p></o:p></p>
</div>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<div>
<div>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">I would like to solve a saddle point problem arising from the stokes equation. I got successful to use the direct solvers in sequential runs. However, I would like to extend it for distributed
memory computation. I tried to use superlu_dist, but the program returns errors. Is it possible to solve a saddle point problem in distributed memory using superlu_dist? Could anyone give a simple sample code to set up the parameters of the solver?</span><o:p></o:p></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif"> </span><o:p></o:p></p>
</div>
</div>
<div>
<div>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif">Thanks</span><o:p></o:p></p>
</div>
</div>
</div>
</blockquote>
</div>
</div>
</div>
</blockquote>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</div>
</div>
</body>
</html>