Optimization of multigrid settings by bigfooted · Pull Request #2772 · su2code/SU2

bigfooted · 2026-03-29T20:13:09Z

Proposed Changes

Give a brief overview of your contribution here in a few sentences.

This PR is an improvement of the multigrid method. The goal is to make it more robust and less sensitive to user-defined settings.
It introduces the following:

When the smoother converges sufficiently, we stop the smoothing and exit the smoother.
This means that the option:

MG_PRE_SMOOTH= ( 5, 5, 5, 5, 5 )
MG_POST_SMOOTH= ( 5, 5, 5, 5, 5 )

effectively becomes the maximum number of iterations that are being performed. The smoothing threshold is given by:
MG_SMOOTH_RES_THRESHOLD=0.5
You can still turn it off using:
MG_SMOOTH_EARLY_EXIT= YES

The damping factors are adaptive. When the smoother converges (exits) within the given number of maximum iterations, the damping factors are increased. When the smoother residuals are larger than the starting residuals, we decrease the damping factor. This means that the option:

MG_DAMP_RESTRICTION= 0.5
MG_DAMP_PROLONGATION= 0.5

effectively becomes a starting damping factor.

Limit the number of MG meshes such that the smallest and coarsest mesh always has more than MG_MIN_MESHSIZE points. This means that the option
MGLEVEL=4
effectively becomes a maximum number of MG levels.
We also expose the smoothing coefficient for correction smoothing to the user:
MG_SMOOTH_COEFF=1.25
fixes multigrid restarts for turbulence problems.

Related Work

Resolve any issues (bug fix or feature request), note any related PRs, or mention interactions with the work of others, if any.
A follow-up to #2712

Will fix #1549

PR Checklist

Put an X by all that apply. You can fill this out after submitting the PR. If you have any questions, don't hesitate to ask! We want to help. These are a guide for you to know what the reviewers will be looking for in your contribution.

I am submitting my contribution to the develop branch.
My contribution generates no new compiler warnings (try with --warnlevel=3 when using meson).
My contribution is commented and consistent with SU2 style (https://su2code.github.io/docs_v7/Style-Guide/).
I used the pre-commit hook to prevent dirty commits and used pre-commit run --all to format old commits.
I have added a test case that demonstrates my contribution, if necessary.
I have updated appropriate documentation (Tutorials, Docs Page, config_template.cpp), if necessary.

SU2_CFD/src/integration/CMultiGridIntegration.cpp

…o feature_MG_adapt

TestCases/serial_regression.py

TestCases/parallel_regression.py

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

…o feature_MG_adapt

Common/include/CConfig.hpp

pcarruscag · 2026-04-03T22:58:40Z

Common/src/geometry/CMultiGridGeometry.cpp

+          su2double vec[MAXNDIM] = {0.0};
+          su2double len2 = 0.0;
+          for (unsigned short d = 0; d < nDim; ++d) {
+            vec[d] = fine_grid->nodes->GetCoord(jPoint, d) - fine_grid->nodes->GetCoord(current, d);
+            len2 += vec[d] * vec[d];
+          }


There is a distance function

this one? GeometryToolbox::Distance

Common/src/geometry/CMultiGridGeometry.cpp

SU2_CFD/src/integration/ComputeLinSysResRMS.hpp

SU2_CFD/src/integration/CMultiGridIntegration.cpp

pcarruscag · 2026-04-03T23:07:21Z

SU2_CFD/src/integration/CMultiGridIntegration.cpp

+      if (iPreSmooth == 0 && iRKStep == 0) {
+        BEGIN_SU2_OMP_SAFE_GLOBAL_ACCESS
+        {
+          lastPreSmoothRMS[iMesh][0] = ComputeLinSysResRMS(solver_fine, geometry_fine);


Don't compute residuals without threads

ok, so computelinsysres outside of the omp loop?

SU2_CFD/src/integration/CMultiGridIntegration.cpp

pcarruscag · 2026-04-03T23:08:35Z

SU2_CFD/src/integration/CMultiGridIntegration.cpp

+    if (early_exit && mg_early_exit_flag) {
+      /*--- Early exit: RMS threshold was met; the RMS that triggered exit is current_rms
+       *    but we don't store it — just do a final read for the output. ---*/
+      lastPreSmoothRMS[iMesh][1] = ComputeLinSysResRMS(solver_fine, geometry_fine);


Actually, why do you need to recompute residuals? Aren't the solvers computing them already?

getRes_RMS only has the fine grid values, this one computes it on all grid levels.

Co-authored-by: Pedro Gomes <38071223+pcarruscag@users.noreply.github.com>

Common/src/CConfig.cpp

pcarruscag · 2026-04-04T20:40:11Z

Common/include/CConfig.hpp

-  bool GetMG_Smooth_EarlyExit() const { return MG_Smooth_EarlyExit; }
+  bool GetMG_Smooth_EarlyExit() const { return MGOptions.MG_Smooth_EarlyExit; }



So the idea is to return a reference to the struct as well, replacing the individual accessors, so that there is just one clean interface for all MG settings.

ok, so we get rid of the individual GetMG_* functions?

@pcarruscag mmm, like this?
const CMGOptions& GetMGOptions() const { return MGOptions; }
and then we can do this for example:
config[iZone]->GetMGOptions().MG_Smooth_EarlyExit)

I looked at sstparsedoptions, and copying that instead, it then looks like this:
const auto& mgOptsZone = config[iZone]->GetMGOptions();
if (mgOptsZone.MG_Smooth_EarlyExit) {

Common/include/option_structure.hpp

bigfooted added 4 commits March 29, 2026 16:48

early exit

5af8875

early exit, post-smoothing improvement

67348fe

smooth coeff

8d28037

add mg_min_meshsize

7a5c019

bigfooted marked this pull request as draft March 29, 2026 20:13

bigfooted added PR: draft changelog:feature labels Mar 29, 2026

bigfooted changed the title ~~Optimization of multigrid settings~~ [WIP] Optimization of multigrid settings Mar 29, 2026

bigfooted added 2 commits March 29, 2026 22:16

precommit

1bafd7a

small cleanup

5830da2

github-advanced-security bot found potential problems Mar 29, 2026

View reviewed changes

SU2_CFD/src/integration/CMultiGridIntegration.cpp Fixed Show fixed Hide fixed

bigfooted added 10 commits March 30, 2026 17:12

Merge branch 'develop' into feature_MG_adapt

7835fa9

change constexpr

45324bc

Merge branch 'feature_MG_adapt' of https://github.com/su2code/su2 int…

b6c4a68

…o feature_MG_adapt

change all multigrid V-cycle setups

bca1a5b

precommit

691cd82

precommit

e9b0049

regressions

296f628

change config settings for better convergence

bbbfc04

fix multigrid restart for turbulence

41a1623

OMP for multigrid restart prevents race

930cf53

bigfooted marked this pull request as ready for review April 1, 2026 20:40

bigfooted changed the title ~~[WIP] Optimization of multigrid settings~~ Optimization of multigrid settings Apr 1, 2026

bigfooted removed the PR: draft label Apr 1, 2026

bigfooted added 2 commits April 2, 2026 22:40

update some regressions

d8c95f8

update some regressions

c478aef

github-advanced-security bot found potential problems Apr 2, 2026

View reviewed changes

TestCases/serial_regression.py Fixed Show fixed Hide fixed

bigfooted added 2 commits April 2, 2026 23:58

update some regressions

e9c968e

update some regressions, change printed output

c503542

github-advanced-security bot found potential problems Apr 3, 2026

View reviewed changes

TestCases/parallel_regression.py Fixed Show fixed Hide fixed

bigfooted and others added 12 commits April 3, 2026 11:15

fix typo

7138418

fix segfault for periodic with multigrid

6b366ce

initial fix for periodic boundaries

cfec822

Potential fix for code scanning alert no. 6209: Syntax error

62650e5

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

Merge branch 'develop' into feature_MG_adapt

4a3a37b

fix additional periodic stuff.

450c768

turbo + MG testcase

8dff939

Merge branch 'feature_MG_adapt' of https://github.com/su2code/su2 int…

fef7613

…o feature_MG_adapt

cleanup matchperiodic

7bde034

cleanup unneeded nan fixes

cda0644

clang

db69ad2

codi

c7f5c25

pcarruscag reviewed Apr 3, 2026

View reviewed changes

bigfooted and others added 7 commits April 4, 2026 08:46

Update SU2_CFD/src/integration/CMultiGridIntegration.cpp

75c337f

Co-authored-by: Pedro Gomes <38071223+pcarruscag@users.noreply.github.com>

Update SU2_CFD/src/integration/CMultiGridIntegration.cpp

24b2c7d

Co-authored-by: Pedro Gomes <38071223+pcarruscag@users.noreply.github.com>

implement review suggestions

862dac7

move and simplify linsysresRMS

10d18f0

use printing toolbox

dcf34d3

use geometry toolbox

bbbbdac

remove allreduce

886ddb3

github-advanced-security bot found potential problems Apr 4, 2026

View reviewed changes

Common/src/CConfig.cpp Fixed Show fixed Hide fixed

Common/src/CConfig.cpp Fixed Show fixed Hide fixed

Common/src/CConfig.cpp Fixed Show fixed Hide fixed

bigfooted added 6 commits April 4, 2026 13:42

fix delete []

2fb12a2

compact mg option initialization

57e0091

remove variable

b22f45b

change su2double to passivedouble to fix tape error

dea3b2b

cleanup, update regression

376d8aa

update regression

e072a59

pcarruscag reviewed Apr 4, 2026

View reviewed changes

Common/include/option_structure.hpp Show resolved Hide resolved

		bool GetMG_Smooth_EarlyExit() const { return MG_Smooth_EarlyExit; }
		bool GetMG_Smooth_EarlyExit() const { return MGOptions.MG_Smooth_EarlyExit; }

Conversation

bigfooted commented Mar 29, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Proposed Changes

Related Work

PR Checklist

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

bigfooted Apr 4, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

bigfooted commented Mar 29, 2026 •

edited

Loading

bigfooted Apr 4, 2026 •

edited

Loading