<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<style type="text/css" style="display:none;"> P {margin-top:0;margin-bottom:0;} </style>
</head>
<body dir="ltr">
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
Hi Barry and Mark,</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0">
Thank you for looking into my problem. The two equations I am solving with PETSc are equations 6 and 7 from this paper:
<a href="https://ris.utwente.nl/ws/portalfiles/portal/5676495/Roghair+Paper_final_draft_v1.pdf" id="LPlnk149320">
https://ris.utwente.nl/ws/portalfiles/portal/5676495/Roghair+Paper_final_draft_v1.pdf</a></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0">
I just used MUMPS and SuperLU_DIST on my full-size problem (with 3,000,000 unknowns). To clarify, I did a direct solve with -ksp_type preonly. They take a very long time, about 30 minutes for MUMPS and 18 minutes for SuperLU_DIST, see attached output. For reference,
the same matrix took 658 iterations of BoomerAMG and about 20 seconds of walltime. Maybe I am already getting a great deal with BoomerAMG!<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0">
I'll try removing some terms from my solve (e.g. removing the second equation, then making the second equation just the elliptic portion of the equation, etc.) and try with a simpler geometry. I'll keep you updated as I run into troubles with that route. I
wasn't aware of Field Split preconditioners, I'll do some reading on them and give them a try as well.<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0">
<br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0">
Thank you again,</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);" class="ContentPasted0">
Joshua<br>
</div>
<div id="appendonsend"></div>
<hr style="display:inline-block;width:98%" tabindex="-1">
<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Barry Smith <bsmith@petsc.dev><br>
<b>Sent:</b> Thursday, March 2, 2023 7:47 AM<br>
<b>To:</b> Christopher, Joshua <jchristopher@anl.gov><br>
<b>Cc:</b> petsc-users@mcs.anl.gov <petsc-users@mcs.anl.gov><br>
<b>Subject:</b> Re: [petsc-users] Overcoming slow convergence with GMRES+Hypre BoomerAMG</font>
<div> </div>
</div>
<div style="line-break:after-white-space">
<div><br>
</div>
Have you tried MUMPS (or SuperLU_DIST) on the full-size problem with the 5,000,000 unknowns? It is at the high end of problem sizes you can do with direct solvers but is worth comparing with BoomerAMG. You likely want to use more nodes and fewer cores per
node with MUMPs to be able to access more memory. If you are needing to solve multiple right hand sides but with the same matrix the factors will be reused resulting in the second and later solves being much faster.
<div><br>
</div>
<div> I agree with Mark, with iterative solvers you are likely to end up with PCFIELDSPLIT.</div>
<div><br>
</div>
<div> Barry</div>
<div><br>
<div><br>
<blockquote type="cite">
<div>On Mar 1, 2023, at 7:17 PM, Christopher, Joshua via petsc-users <petsc-users@mcs.anl.gov> wrote:</div>
<br class="x_Apple-interchange-newline">
<div>
<div style="font-style:normal; font-variant-caps:normal; font-weight:400; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none; font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; background-color:rgb(255,255,255)">
Hello,</div>
<div style="font-style:normal; font-variant-caps:normal; font-weight:400; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none; font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; background-color:rgb(255,255,255)">
<br>
</div>
<div class="x_ContentPasted0 x_ContentPasted1" style="font-style:normal; font-variant-caps:normal; font-weight:400; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none; font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; background-color:rgb(255,255,255)">
I am trying to solve the leaky-dielectric model equations with PETSc using a second-order discretization scheme (with limiting to first order as needed) using the finite volume method. The leaky dielectric model is a coupled system of two equations, consisting
of a Poisson equation and a convection-diffusion equation. I have tested on small problems with simple geometry (~1000 DoFs) using:<br>
<br>
-ksp_type gmres<span class="x_Apple-converted-space"> </span><br>
-pc_type hypre<span class="x_Apple-converted-space"> </span><br>
-pc_hypre_type boomeramg<br>
<br>
and I get RTOL convergence to 1.e-5 in about 4 iterations. I tested this in parallel with 2 cores, but also previously was able to use successfully use a direct solver in serial to solve this problem. When I scale up to my production problem, I get significantly
worse convergence. My production problem has ~3 million DoFs, more complex geometry, and is solved on ~100 cores across two nodes. The boundary conditions change a little because of the geometry, but are of the same classifications (e.g. only Dirichlet and
Neumann). On the production case, I am needing 600-4000 iterations to converge. I've attached the output from the first solve that took 658 iterations to converge, using the following output options:<br>
</div>
<div class="x_ContentPasted0 x_ContentPasted1" style="font-style:normal; font-variant-caps:normal; font-weight:400; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none; font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; background-color:rgb(255,255,255)">
<br>
</div>
<div class="x_ContentPasted0 x_ContentPasted1 x_ContentPasted2" style="font-style:normal; font-variant-caps:normal; font-weight:400; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none; font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; background-color:rgb(255,255,255)">
-ksp_view_pre
<div class="x_ContentPasted2">-ksp_view</div>
<div class="x_ContentPasted2">-ksp_converged_reason</div>
<div class="x_ContentPasted2">-ksp_monitor_true_residual</div>
-ksp_test_null_space</div>
<div class="x_ContentPasted0 x_ContentPasted1 x_ContentPasted2" style="font-style:normal; font-variant-caps:normal; font-weight:400; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none; font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; background-color:rgb(255,255,255)">
<br>
</div>
<div class="x_ContentPasted0 x_ContentPasted1 x_ContentPasted2 x_ContentPasted3" style="font-style:normal; font-variant-caps:normal; font-weight:400; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none; font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; background-color:rgb(255,255,255)">
My matrix is non-symmetric, the condition number can be around 10e6, and the eigenvalues reported by PETSc have been real and positive (using -ksp_view_eigenvalues).<span class="x_Apple-converted-space"> </span><br>
<br>
I have tried using other preconditions (superlu, mumps, gamg, mg) but hypre+boomeramg has performed the best so far. The literature seems to indicate that AMG is the best approach for solving these equations in a coupled fashion.</div>
<div class="x_ContentPasted0 x_ContentPasted1 x_ContentPasted2 x_ContentPasted3" style="font-style:normal; font-variant-caps:normal; font-weight:400; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none; font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; background-color:rgb(255,255,255)">
<br>
</div>
<div class="x_ContentPasted0 x_ContentPasted1 x_ContentPasted2 x_ContentPasted3" style="font-style:normal; font-variant-caps:normal; font-weight:400; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none; font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; background-color:rgb(255,255,255)">
Do you have any advice on speeding up the convergence of this system?<span class="x_Apple-converted-space"> </span><br>
</div>
<div class="x_ContentPasted0 x_ContentPasted1 x_ContentPasted2 x_ContentPasted3" style="font-style:normal; font-variant-caps:normal; font-weight:400; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none; font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; background-color:rgb(255,255,255)">
<br>
</div>
<div class="x_ContentPasted0 x_ContentPasted1 x_ContentPasted2 x_ContentPasted3" style="font-style:normal; font-variant-caps:normal; font-weight:400; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none; font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; background-color:rgb(255,255,255)">
Thank you,</div>
<div class="x_ContentPasted0 x_ContentPasted1 x_ContentPasted2 x_ContentPasted3" style="font-style:normal; font-variant-caps:normal; font-weight:400; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none; font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; background-color:rgb(255,255,255)">
Joshua<br>
</div>
<span id="x_cid:B8340654-41D9-48B9-80BA-1D987A4CB56A"><petsc_gmres_boomeramg.txt></span></div>
</blockquote>
</div>
<br>
</div>
</div>
</body>
</html>