Support single-level multigrid (maxLevels = 1) when extrapolation is disabled by julianlitz · Pull Request #179 · SciCompMod/GMGPolar

julianlitz · 2026-02-17T20:04:21Z

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julianlitz · 2026-02-17T20:07:25Z

include/GMGPolar/setup.h

+    // ------------------------------------------------ //
+    // Define residual operator on all multigrid levels //
+    // ------------------------------------------------ //
    for (int level_depth = 0; level_depth < number_of_levels_; level_depth++) {
-        // ---------------------- //
-        // Level 0 (finest Level) //
-        // ---------------------- //
-        if (level_depth == 0) {
-            auto start_setup_smoother = std::chrono::high_resolution_clock::now();
-            switch (extrapolation_) {
-            case ExtrapolationType::NONE:
-                full_grid_smoothing_ = true;
-                levels_[level_depth].initializeSmoothing(domain_geometry_, density_profile_coefficients_,
-                                                         DirBC_Interior_, max_omp_threads_,
-                                                         stencil_distribution_method_);
-                break;
-            case ExtrapolationType::IMPLICIT_EXTRAPOLATION:
-                full_grid_smoothing_ = false;
-                levels_[level_depth].initializeExtrapolatedSmoothing(domain_geometry_, density_profile_coefficients_,
-                                                                     DirBC_Interior_, max_omp_threads_,
-                                                                     stencil_distribution_method_);
-                break;
-            case ExtrapolationType::IMPLICIT_FULL_GRID_SMOOTHING:
-                full_grid_smoothing_ = true;
-                levels_[level_depth].initializeSmoothing(domain_geometry_, density_profile_coefficients_,
-                                                         DirBC_Interior_, max_omp_threads_,
-                                                         stencil_distribution_method_);
-                break;
-            case ExtrapolationType::COMBINED:
-                full_grid_smoothing_ = true;
-                levels_[level_depth].initializeSmoothing(domain_geometry_, density_profile_coefficients_,
-                                                         DirBC_Interior_, max_omp_threads_,
-                                                         stencil_distribution_method_);
-                levels_[level_depth].initializeExtrapolatedSmoothing(domain_geometry_, density_profile_coefficients_,
-                                                                     DirBC_Interior_, max_omp_threads_,
-                                                                     stencil_distribution_method_);
-                break;
-            default:
-                full_grid_smoothing_ = false;
-                levels_[level_depth].initializeSmoothing(domain_geometry_, density_profile_coefficients_,
-                                                         DirBC_Interior_, max_omp_threads_,
-                                                         stencil_distribution_method_);
-                levels_[level_depth].initializeExtrapolatedSmoothing(domain_geometry_, density_profile_coefficients_,
-                                                                     DirBC_Interior_, max_omp_threads_,
-                                                                     stencil_distribution_method_);
-                break;
-            }
-            auto end_setup_smoother = std::chrono::high_resolution_clock::now();
-            t_setup_smoother_ += std::chrono::duration<double>(end_setup_smoother - start_setup_smoother).count();
-            levels_[level_depth].initializeResidual(domain_geometry_, density_profile_coefficients_, DirBC_Interior_,
-                                                    max_omp_threads_, stencil_distribution_method_);
+        levels_[level_depth].initializeResidual(domain_geometry_, density_profile_coefficients_, DirBC_Interior_,
+                                                max_omp_threads_, stencil_distribution_method_);
+    }


Extract Residual initialization

julianlitz · 2026-02-17T20:07:37Z

include/GMGPolar/setup.h

+    // ----------------------------------------- //
+    // Build direct solver on the coarsest level //
+    // ----------------------------------------- //
+    auto start_setup_directSolver = std::chrono::high_resolution_clock::now();
+    levels_[number_of_levels_ - 1].initializeDirectSolver(domain_geometry_, density_profile_coefficients_,
+                                                          DirBC_Interior_, max_omp_threads_,
+                                                          stencil_distribution_method_);
+    auto end_setup_directSolver = std::chrono::high_resolution_clock::now();
+    t_setup_directSolver_ += std::chrono::duration<double>(end_setup_directSolver - start_setup_directSolver).count();


Extract DirectSolver initialization

julianlitz · 2026-02-17T20:07:57Z

include/GMGPolar/setup.h

+    // ---------------------------------------------------------- //
+    // Build the full-grid smoother and the extrapolated smoother //
+    // ---------------------------------------------------------- //
+    auto start_setup_smoother = std::chrono::high_resolution_clock::now();
+
+    bool do_full_grid_smoothing    = false;
+    bool do_extrapolated_smoothing = false;
+
+    switch (extrapolation_) {
+
+    case ExtrapolationType::NONE:
+        do_full_grid_smoothing = true;
+        break;
+
+    case ExtrapolationType::IMPLICIT_EXTRAPOLATION:
+        do_extrapolated_smoothing = true;
+        break;
+
+    case ExtrapolationType::IMPLICIT_FULL_GRID_SMOOTHING:
+        do_full_grid_smoothing = true;
+        break;
+
+    case ExtrapolationType::COMBINED:
+        do_full_grid_smoothing    = true;
+        do_extrapolated_smoothing = true;
+        break;
+    }
+
+    full_grid_smoothing_ = do_full_grid_smoothing;
+
+    if (number_of_levels_ > 1) {
+        if (do_full_grid_smoothing) {
+            levels_[0].initializeSmoothing(domain_geometry_, density_profile_coefficients_, DirBC_Interior_,
+                                           max_omp_threads_, stencil_distribution_method_);
        }
-        // -------------------------- //
-        // Level n-1 (coarsest Level) //
-        // -------------------------- //
-        else if (level_depth == number_of_levels_ - 1) {
-            auto start_setup_directSolver = std::chrono::high_resolution_clock::now();
-            levels_[level_depth].initializeDirectSolver(domain_geometry_, density_profile_coefficients_,
-                                                        DirBC_Interior_, max_omp_threads_,
-                                                        stencil_distribution_method_);
-            auto end_setup_directSolver = std::chrono::high_resolution_clock::now();
-            t_setup_directSolver_ +=
-                std::chrono::duration<double>(end_setup_directSolver - start_setup_directSolver).count();
-            levels_[level_depth].initializeResidual(domain_geometry_, density_profile_coefficients_, DirBC_Interior_,
-                                                    max_omp_threads_, stencil_distribution_method_);
+        if (do_extrapolated_smoothing) {
+            levels_[0].initializeExtrapolatedSmoothing(domain_geometry_, density_profile_coefficients_, DirBC_Interior_,
+                                                       max_omp_threads_, stencil_distribution_method_);
        }
-        // ------------------- //
-        // Intermediate levels //
-        // ------------------- //
-        else {
-            auto start_setup_smoother = std::chrono::high_resolution_clock::now();
+        for (int level_depth = 1; level_depth < number_of_levels_ - 1; level_depth++) {
            levels_[level_depth].initializeSmoothing(domain_geometry_, density_profile_coefficients_, DirBC_Interior_,
                                                     max_omp_threads_, stencil_distribution_method_);
-            auto end_setup_smoother = std::chrono::high_resolution_clock::now();
-            t_setup_smoother_ += std::chrono::duration<double>(end_setup_smoother - start_setup_smoother).count();
-            levels_[level_depth].initializeResidual(domain_geometry_, density_profile_coefficients_, DirBC_Interior_,
-                                                    max_omp_threads_, stencil_distribution_method_);
        }
    }


Extract Smoother initialization. Simpler to read.

julianlitz · 2026-02-17T20:08:59Z

src/GMGPolar/MultigridMethods/multigrid_F_Cycle.cpp

+void IGMGPolar::multigrid_F_Cycle(int level_depth, Vector<double> solution, ConstVector<double> rhs,
+                                  Vector<double> residual)
 {
-    assert(0 <= level_depth && level_depth < number_of_levels_ - 1);
+    assert(0 <= level_depth && level_depth < number_of_levels_);

    std::chrono::high_resolution_clock::time_point start_MGC;
    if (level_depth == 0) {
        start_MGC = std::chrono::high_resolution_clock::now();
    }

-    Level& level      = levels_[level_depth];
-    Level& next_level = levels_[level_depth + 1];
+    /* ------------------------ */
+    /* Solve A * solution = rhs */
+    /* ------------------------ */
+    if (level_depth == number_of_levels_ - 1) {
+        /* ------------------------------ */
+        /* Coarsest level: solve directly */
+        /* ------------------------------ */


We can now also solve on level_depth = 0 directly, which was not possible before.
For this I moved some code sections around.

julianlitz · 2026-02-17T20:10:25Z

src/GMGPolar/setup.cpp


    // Minimum level for Multigrid
-    const int multigridMinLevel = 2;
+    const int multigridMinLevel = (extrapolation_ == ExtrapolationType::NONE) ? 1 : 2;


With extrapolation=None, we are now able to choose maxLevels=1.

julianlitz · 2026-02-17T20:12:50Z

include/GMGPolar/setup.h

-            throw std::runtime_error(
-                "Extrapolation Error: Finest PolarGrid does not originate from a single uniform refinement.");


Abort immediately may not be a good idea. Better replace by a warning?

julianlitz · 2026-02-17T20:13:31Z

include/GMGPolar/setup.h

-    int level_depth        = 0;
    auto finest_levelCache = std::make_unique<LevelCache>(*finest_grid, density_profile_coefficients_, domain_geometry_,
                                                          cache_density_profile_coefficients_, cache_domain_geometry_);
-    levels_.emplace_back(level_depth, std::move(finest_grid), std::move(finest_levelCache), extrapolation_, FMG_);


Avoid variable shadowing in later loops.

codecov · 2026-02-17T20:14:58Z

Codecov Report

❌ Patch coverage is 94.19355% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.25%. Comparing base (8ba043e) to head (ae29cb9).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...ultigridMethods/extrapolated_multigrid_W_Cycle.cpp	11.11%	8 Missing ⚠️
include/GMGPolar/setup.h	97.22%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #179      +/-   ##
==========================================
+ Coverage   95.11%   95.25%   +0.13%     
==========================================
  Files          95       95              
  Lines        9458     9460       +2     
==========================================
+ Hits         8996     9011      +15     
+ Misses        462      449      -13

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maxLevel = 1 now allowed without extrapolation

ae29cb9

julianlitz commented Feb 17, 2026

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julianlitz requested a review from EmilyBourne February 17, 2026 20:16

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Support single-level multigrid (maxLevels = 1) when extrapolation is disabled#179

Support single-level multigrid (maxLevels = 1) when extrapolation is disabled#179
julianlitz wants to merge 1 commit intomainfrom
litz_allow_no_mg

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		throw std::runtime_error(
		"Extrapolation Error: Finest PolarGrid does not originate from a single uniform refinement.");

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julianlitz commented Feb 17, 2026

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