Agglomeration Multigrid and Full Multigrid
NeuralFlow exposes both an ongoing agglomeration-multigrid solver and full-multigrid (FMG) initialization. Coarse levels represent groups of fine cells so long-wavelength error can be reduced much faster than by fine-grid iterations alone.
Theory reference. Each option entry includes a link to the corresponding equation, physical model, closure, or numerical method in the Theory Manual. Defaults, availability, simulation effects, and practical guidance are documented directly with the GUI option.
Two different controls contain “FMG”. The FMG cycle in the ongoing cycle schedule is a multigrid correction pattern during a normal solve. Full Multigrid initialization is a separate procedure that builds an initial flow field from coarse to fine levels.
Hierarchy construction
Hierarchy controls define how the fine mesh is agglomerated into coarse levels.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Enable agglomeration multigridDefault: Off unless selected | Activates the geometric agglomeration multigrid hierarchy and recursive coarse-grid correction. | Stability / convergenceCost Can reduce low-frequency nonlinear/algebraic error much faster than single-grid iteration, but adds hierarchy memory and coarse-grid work. | Use on medium/large meshes when single-grid convergence stalls or becomes expensive. | Multigrid hierarchy |
| Target coarsest cellsDefault: 500 | Requests a coarse-grid size near the specified cell count. Coarsening stops when the target or other hierarchy limits are reached. | Stability / convergenceCost Smaller targets permit deeper/coarser error correction but may create low-quality aggregates or diminishing returns. | Use a few hundred cells as a starting scale for large cases; inspect the actual hierarchy. | Multigrid hierarchy |
| Maximum levels (level 0 included)Default: 5 | Caps total hierarchy depth; level 0 is always the original fine mesh. | Stability / convergenceCost More levels can improve long-wavelength error removal but increase setup/storage and can expose poorer coarse geometry. | Use the built-level table rather than assuming all requested levels are created. | Multigrid hierarchy |
| Base agglomerator: Default agglomeratorDefault: Default | Uses the compatibility/default coarse-cell grouping method. | Stability / convergenceCost Defines the initial fine-to-coarse mapping and therefore coarse geometry, operator quality and multigrid efficiency. | Recommended starting choice for established cases. | Multigrid hierarchy |
| Base agglomerator: Alternative agglomerator | Uses the alternative coarse-cell grouping method available in the GUI. | Stability / convergenceCost May produce a different hierarchy quality and convergence rate for difficult meshes. | Compare hierarchy diagnostics and solve performance before changing production cases. | Multigrid hierarchy |
| Base agglomerator: Strict best-admissible comparison | Builds both available candidate mappings, requires admissible results, evaluates their finite-volume quality, and keeps the better candidate. | Stability / convergenceCost Higher hierarchy-build cost but can improve robustness/quality on difficult meshes. | Use when hierarchy quality is more important than setup time. | Multigrid hierarchy |
| Coarse-grid creation refinement: NoneDefault: Default | Keeps the raw base mapping. | Cost Fastest hierarchy creation; no extra local search for improved aggregate quality. | Use as baseline/default. | Multigrid hierarchy |
| Quality-constrained local refinement | Performs deterministic local moves/swaps while preserving admissibility to improve the coarse-grid quality objective. | Stability / convergenceCost Increases setup time and may reduce poor local aggregate geometry. | Use when diagnostics show isolated hierarchy-quality problems. | Multigrid hierarchy |
| Quality-constrained patch refinement | Applies stronger connected-patch optimization after the base mapping is valid. | Stability / convergenceCost Higher setup cost and broader local changes can improve difficult coarse regions. | Use when local refinement is insufficient. | Multigrid hierarchy |
| Hybrid directional + patch refinement | Adds directional/anisotropy-aware candidates before patch refinement. | Stability / convergenceCost Can improve hierarchy quality on highly stretched/anistropic meshes but has the greatest setup cost among refinement choices. | Consider for strong boundary-layer/grid-stretching cases after inspecting coarse-grid warnings. | Multigrid hierarchy |
| Maximum refinement passesDefault: 4 (active only with refinement) | Caps deterministic hierarchy-refinement sweeps; search stops earlier if no admissible improvement is accepted. This field is enabled only when a refinement mode other than None is selected. | Stability / convergenceCost Higher values allow more hierarchy-setup work in pursuit of better coarse geometry; it has no effect when refinement is None. | Increase only when additional passes continue improving diagnostics or multigrid performance. | Multigrid hierarchy |
| Coarse-grid quality: Warn and mark onlyDefault: Default | Always diagnoses quality but retains the created mapping and marks warnings. | Stability / convergenceReporting / display Preserves hierarchy even with warning-level geometry; poor levels can reduce multigrid effectiveness. | Good default while inspecting a new hierarchy. | Multigrid hierarchy |
| Coarse-grid quality: Automatically protect/repair | Enables available protection/repair actions for warning regions. | Stability / convergenceCost Adds setup work but can improve coarse-level robustness. | Use when warnings correlate with multigrid instability or slow convergence. | Multigrid hierarchy |
| Coarse-grid quality: Repair and reject unresolved levels | Repairs where possible and truncates/rejects coarse levels that remain unresolved. | Stability / convergenceCost Most conservative quality policy; may reduce hierarchy depth but avoids using problematic coarse levels. | Use for production robustness when unresolved warnings cause failures. | Multigrid hierarchy |
| Build / rebuild hierarchy | Constructs the hierarchy using the current mesh and hierarchy settings. | InitializationCost Changes active coarse-grid data, not the fine-grid physical model. | Rebuild after mesh, zone, quality-policy or hierarchy-setting changes. | Multigrid hierarchy |
| Print built level table | Reports the actual retained levels and global cell/face counts. | Reporting / display No solution change. | Check after every new hierarchy to verify coarsening is sensible. | Multigrid hierarchy |
Hierarchy quality diagnostic thresholds
These fields classify coarse-grid warnings. They do not change the fine-grid physical equations directly.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Maximum non-orthogonality | Warning threshold in degrees for transmissive coarse faces. | Stability / convergenceReporting / display Classifies poor angular alignment that can degrade coarse discretization and interpolation. | Lower thresholds are stricter; use diagnostics to identify problematic coarse levels. | Multigrid hierarchy |
| Maximum closure residual | Maximum dimensionless area-vector closure error used for coarse-cell quality diagnosis. | Stability / convergenceReporting / display Large closure error indicates inconsistent coarse geometry and can degrade conservation/operator quality. | Treat persistent large closure warnings as a hierarchy-quality issue. | Multigrid hierarchy |
| Minimum face weight | Minimum allowed normal-distance interpolation weight on transmissive coarse faces. | Stability / convergenceReporting / display Very small weights indicate strongly biased geometry and can weaken interpolation/discretization quality. | Use as a warning/repair threshold rather than a physics parameter. | Multigrid hierarchy |
| Minimum neighboring-cell volume ratio | Minimum smaller-to-larger volume ratio across a transmissive coarse face. | Stability / convergenceReporting / display Flags abrupt coarse-cell size jumps that can harm coarse-grid correction quality. | Tighten only if abrupt aggregate-size transitions are problematic. | Multigrid hierarchy |
| Minimum composite-face area ratio | Uses | Stability / convergenceReporting / display Low ratio indicates poorly aligned constituent faces and a weak resultant coarse face. | Use warnings to guide refinement/repair choices. | Multigrid hierarchy |
| Maximum face-centre skew ratio | Bounds face-centre displacement from the adjacent-cell line/face-plane intersection, normalized by local cell length. | Stability / convergenceReporting / display Large skew can reduce coarse operator accuracy/robustness. | Keep diagnostic limits consistent across hierarchy comparisons. | Multigrid hierarchy |
| Maximum aggregate aspect ratio | Bounds the ratio of largest to smallest aggregate-centre-to-face-centre radii. | Stability / convergenceReporting / display Flags strongly elongated coarse cells; excessive aspect ratio can weaken smoothing/coarse correction. | Especially relevant for stretched meshes; combine with directional refinement if needed. | Multigrid hierarchy |
AggMG solver controls
These controls determine how much work each multigrid cycle performs.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Multigrid formulation: Nonlinear FASDefault: Recommended/default | Uses the full approximation scheme. Conceptually, the coarse problem includes the restricted fine approximation and a forcing correction so the nonlinear coarse equation is consistent with the fine-grid defect. | Stability / convergenceCost Best suited to the nonlinear coupled NeuralFlow equations and recommended for production multigrid. | Use as the normal AggMG formulation. | Nonlinear FAS |
| Multigrid formulation: Implicit linear correction | Forms coarse correction equations for the linearized problem. | Stability / convergenceCost Can be useful for comparison or problems where linearized multigrid behavior is preferred; nonlinear error transfer is less direct than FAS. | Use mainly for solver-method comparisons or validated workflows. | Correction multigrid |
| Multigrid formulation: Legacy hybrid | Retained compatibility path restricted to V-cycle behavior. | Stability / convergence Not the recommended general solver path. | Use only for reproducing older cases that explicitly require it. | Current multigrid controls |
| Number of AggMG iterationsDefault: 20 typical option default | Number of completed top-level multigrid cycles requested when solving. | Cost More cycles permit further nonlinear convergence and increase cost. | Stop based on residual/engineering convergence, not a fixed cycle count alone. | Current multigrid controls |
| Smoother KSP cap / coarse sweepsDefault: 3 | Caps noncoarsest smoother Krylov work and sets full implicit sweep effort at the coarsest level. | Stability / convergenceCost More smoothing reduces high-frequency error per visit but makes each cycle more expensive. | Increase if coarse correction is good but local/high-frequency error remains; reduce if cycles are too expensive. | Current multigrid controls |
| Scaled defect toleranceDefault: 1e-3 | Stops a recursive branch when its scaled algebraic defect reaches the tolerance. | Stability / convergenceCost Tighter values spend more work on coarse branches; looser values make cycles cheaper but less complete. | Use enough accuracy that coarse solves do not become the convergence bottleneck. | Current multigrid controls |
| Coarse-level CFLDefault: 5 | Pseudo-time CFL used while rediscretizing/smoothing coarse equations. | Stability / convergenceCost Higher values can accelerate coarse correction but may destabilize poor coarse grids. | Keep moderate; reduce if coarse-level nonlinear failures occur. | Current multigrid controls |
| Apply AggMG options | Commits the displayed formulation, cycle, smoothing, tolerance, CFL and prolongation choices. | Initialization Changes subsequent multigrid behavior. | Apply before solving after editing AggMG controls. | Current multigrid controls |
Cycle schedule and correction prolongation
Cycle type sets recursive work; prolongation determines how a coarse correction is returned to child cells.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| V-cycleDefault: Selected initially | Visits each coarser level once on a recursive descent/ascent. | Stability / convergenceCost Lowest work per cycle; often best efficiency when coarse correction is already effective. | Start with V-cycle. | Cycle schedule |
| W-cycle | Visits coarse levels twice with an updated remaining defect. | Stability / convergenceCost More expensive but stronger coarse correction, useful for difficult low-frequency error. | Use if V-cycles reduce residual too slowly despite good hierarchy quality. | Cycle schedule |
| F-cycle | Uses an F-pattern followed by a V visit at each level. | Stability / convergenceCost Intermediate/stronger coarse work than a simple V-cycle. | Consider for difficult startup or deep hierarchies. | Cycle schedule |
| FMG cycle (ongoing-solve schedule) | Uses the FMG-style correction schedule during an ongoing normal solution; it is not the standalone initializer. | Stability / convergenceCost Changes recursive visit pattern and work per top-level cycle. | Do not confuse with “Initialize with Full Multigrid”. | Cycle schedule |
| Piecewise-constant injection | Every child receives its parent coarse correction. | Stability / convergenceAccuracy Most robust/simple transfer but creates piecewise-constant correction jumps and can be less accurate. | Useful as a fallback or diagnostic transfer. | Correction prolongation |
| Inverse-distance interpolation (IDW-1) | Blends parent and neighboring coarse corrections with positive inverse-distance weights. | AccuracyStability / convergence Smoother correction transfer and potentially better convergence; depends on coarse geometry. | Good moderate interpolation choice. | Correction prolongation |
| Corrected / localized interpolationDefault: Selected initially | Uses corrected interpolation for nonlinear FAS and localized higher-order inverse-distance behavior for linear correction. | AccuracyStability / convergence Can improve coarse-to-fine correction accuracy and convergence but is more sensitive to geometry/admissibility. | Recommended default when hierarchy quality is good. | Correction prolongation |
Full Multigrid initialization
FMG is an initialization strategy, not a different final set of governing equations.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Initialization method: Robust FMGDefault: Default method | Uses the coupled nonlinear implicit FAS initialization path, moving from the coarsest usable level toward the fine grid with state checks and retries. | InitializationStability / convergenceCost Can create a much better global initial field than fine-grid-only startup, especially for elliptic/low-frequency error. | Recommended general FMG initializer. | Full-multigrid initialization |
| Initialization method: Explicit FAS FMG | Uses the alternate explicit multi-stage FAS initialization path with local pseudo-time and smoothing. | InitializationStability / convergenceCost Avoids an implicit linear solve during this initialization mode; can be useful for laminar/inviscid startup but has different robustness/cost behavior. | Use as an alternate initializer when appropriate for the active physics. | Full-multigrid initialization |
| FMG preset: RobustDefault: Default preset | Loads conservative hierarchy, CFL, retry, transfer and cleanup settings. | InitializationStability / convergence Prioritizes successful initialization over minimum work. | General starting preset. | Full-multigrid initialization |
| FMG preset: High-Speed | Loads more conservative startup settings intended for strong compressibility/high-speed states. | InitializationStability / convergenceCost Smaller CFL/positivity steps improve robustness but increase initialization work. | Use for shocks, nozzles and high pressure-ratio/high-Mach starts. | Full-multigrid initialization |
| FMG preset: SST Wall-Bounded | Loads settings with additional wall/turbulence cleanup for wall-bounded turbulent cases. | InitializationStability / convergenceCost Adds work to establish turbulence/wall state after coarse-to-fine transfer. | Use for GE-RANS wall-bounded starts. | Full-multigrid initialization |
| FMG preset: Custom | Allows the advanced fields to be edited independently. | InitializationStability / convergence Gives full control; inconsistent combinations can reduce robustness. | Use after understanding the preset behavior and changing one factor at a time. | Full-multigrid initialization |
| Automatic hierarchyDefault: On in robust setup | Allows FMG to select/use the available hierarchy depth automatically. | InitializationStability / convergence Avoids forcing unusable coarse levels. | Keep enabled unless a controlled level-count study is required. | Full-multigrid initialization |
| Robust FMG maximum total levelsDefault: 5 | Caps total levels used by robust FMG. | InitializationCost More levels can improve global initialization but add transfer/coarse work and depend on hierarchy quality. | Use the smallest depth that gives fast robust startup. | Full-multigrid initialization |
| Explicit FAS maximum coarse levelsDefault: 5 | Caps coarse depth for the explicit initializer. | InitializationCost Controls initialization work and geometry exposure. | Keep moderate on difficult meshes. | Full-multigrid initialization |
| Explicit FAS coarsen byDefault: 2 | Controls nominal coarsening ratio/stride used by the explicit initialization hierarchy logic. | InitializationStability / convergence Larger values coarsen more aggressively and reduce levels but can weaken coarse representation. | Keep the established value unless testing hierarchy sensitivity. | Full-multigrid initialization |
| Deeper-level CFL factorDefault: 0.90 | Applies a multiplier per level below the active explicit FAS level, e.g. | InitializationStability / convergence Values below 1 make deeper coarse levels more conservative. | Keep below or near 1; reduce if deep-level states are rejected. | Full-multigrid initialization |
| Residual reduction targetDefault: 1e-3 | Target ratio | InitializationCost Smaller target improves each level more before transfer but costs more cycles. | Use around the robust default, then check whether tighter targets improve fine-level startup. | Full-multigrid initialization |
| Per-level residual targetsDefault: Blank = global target | Optional comma-separated level-specific convergence targets; missing entries fall back to the global target. | InitializationCost Lets coarse/fine levels receive different effort. | Leave blank initially; customize only when one level consistently dominates work. | Full-multigrid initialization |
| Per-level maximum cyclesDefault: 100, 200, 400, 800, 800, ... | Maximum FAS cycle budget per level; last entry is reused for additional levels. | InitializationCost Caps runaway initialization work at a level. | Increase only if a level is making steady progress but hits its budget. | Full-multigrid initialization |
| FMG check intervalDefault: 10 | How often FMG evaluates/report convergence/divergence/stagnation (first cycle is always checked). | InitializationReporting / display Smaller interval gives faster detection/reporting with slightly more checking overhead. | Default is suitable for most cases. | Full-multigrid initialization |
| Initial FMG CFLDefault: Robust 0.75; High-Speed 0.35; SST Wall-Bounded 0.50 | Starting pseudo-time CFL used by the FMG initializer before adaptive growth/reduction. | InitializationStability / convergenceCost Larger values make initialization more aggressive and faster when accepted, but increase the risk of state rejection or divergence. | Use a preset first; reduce for difficult high-speed or strongly coupled starts. | Full-multigrid initialization |
| Minimum FMG CFLDefault: Robust 0.05; High-Speed 0.01; SST Wall-Bounded 0.025 | Lower recovery bound for the adaptive FMG CFL. | InitializationStability / convergenceCost A smaller minimum gives the initializer more room to recover from rejected updates, at the cost of potentially slow progress. | Do not raise this aggressively on difficult cases. | Full-multigrid initialization |
| Maximum FMG CFLDefault: Robust 3; High-Speed 1; SST Wall-Bounded 2 | Upper adaptive FMG CFL bound. | InitializationStability / convergenceCost Limits the maximum aggressiveness of accepted initialization updates. | Raise only after the initializer is demonstrably robust. | Full-multigrid initialization |
| FMG CFL reduction factorDefault: 0.5 | Multiplies CFL after a rejected/failed update. | InitializationStability / convergence Smaller values recover more aggressively but can slow progress after a rejection. | Use the preset value unless retry behavior shows a clear need to change it. | Full-multigrid initialization |
| FMG CFL growth factorDefault: Robust 1.15; High-Speed 1.10; SST Wall-Bounded 1.12 | Multiplies CFL as accepted progress permits. | InitializationStability / convergenceCost Larger values accelerate growth but can create repeated overshoot/rejection. | Use gradual growth, especially for shock/high-pressure-ratio startup. | Full-multigrid initialization |
| FMG positivity update rateDefault: Robust 0.20; High-Speed 0.10; SST Wall-Bounded 0.15 | Limits initialization correction magnitude to preserve admissible positive states. | InitializationStability / convergence Smaller values make startup more conservative and robust, but require more accepted steps. | Use the more conservative high-speed value for strong shocks or large thermodynamic changes. | Full-multigrid initialization |
| Maximum rejected retriesDefault: Robust 8; High-Speed 7; SST Wall-Bounded 8 | Maximum number of reduced-CFL retries allowed after rejected updates at a level. | InitializationStability / convergenceCost More retries improve recovery chance but can spend substantial time on a fundamentally poor setup/hierarchy. | If this cap is repeatedly reached, inspect boundary/initial state and hierarchy quality rather than only raising it. | Full-multigrid initialization |
| Pre-relaxation sweepsDefault: 1 | Explicit relaxation passes before restriction in the explicit FAS initializer. | InitializationCost More sweeps reduce local/high-frequency error before coarse correction at added cost. | One is the normal starting point. | Full-multigrid initialization |
| Post-relaxation sweepsDefault: 0 | Explicit relaxation passes after prolongation on intermediate levels. | InitializationCost Can smooth transfer-induced error but costs more; zero avoids unnecessary post-work in the standard explicit pattern. | Increase only if prolongated corrections create oscillatory local error. | Full-multigrid initialization |
| Residual smoothing iterationsDefault: 2 | Number of smoothing passes applied to the finite-volume residual before explicit FMG stages. | InitializationStability / convergenceCost More passes damp high-frequency residual noise but increase work and can over-smooth useful local information. | Increase only if residual noise, rather than a physics/setup problem, limits explicit initialization. | Full-multigrid initialization |
| Residual smoothing factorDefault: 0.5 | Strength of each residual-smoothing pass. | InitializationStability / convergenceCost A larger value smooths more strongly; too much can smear meaningful local residual structure. | Keep the moderate default unless a controlled sensitivity test supports a change. | Full-multigrid initialization |
| Correction smoothing iterationsDefault: 2 | Number of smoothing passes applied after coarse correction transfer. | InitializationStability / convergenceCost More passes reduce aggregate-boundary jumps but add cost and can diffuse a useful correction. | Use the smallest number that removes transfer artifacts. | Full-multigrid initialization |
| Correction smoothing factorDefault: 0.5 | Strength of each correction-smoothing pass. | InitializationStability / convergenceCost Controls how strongly neighboring fine-cell corrections are blended after transfer. | Keep modest; excessive smoothing weakens coarse-grid correction. | Full-multigrid initialization |
| FMG physics: Proven Nonlinear FAS FMG | Uses the robust mean-flow FMG physics treatment. | InitializationPhysicsStability / convergence Prioritizes established coarse-to-fine initialization behavior. | General choice. | Full-multigrid initialization |
| FMG physics: Full-Physics Nonlinear FAS FMG | Keeps the full viscous/wall-relevant physics treatment active through the FMG initialization path. | InitializationPhysicsCost More faithful for strongly wall/viscous-coupled starts but can be stiffer and costlier. | Use when wall/viscous physics cannot be deferred during initialization. | Full-multigrid initialization |
| Full-state transfer: Conservative injection | Transfers the complete conservative state from parent to child without interpolation. | InitializationStability / convergence Most robust/admissible but least smooth. | Use as robust fallback. | Full-multigrid initialization |
| Full-state transfer: Conservative IDW-1 variation | Uses conservative inverse-distance variation during full-state transfer. | InitializationAccuracyStability / convergence Smoother initial fine state with more geometry dependence. | Use when hierarchy quality is good. | Full-multigrid initialization |
| Full-state transfer: Conservative IDW-2 variation | Uses the higher-order/localized conservative transfer variation. | InitializationAccuracyStability / convergence Can improve fine-field quality but is more likely to require admissibility fallback. | Use with fallback enabled for difficult cases. | Full-multigrid initialization |
| Fallback to conservative injectionDefault: On in robust setup | If an interpolated transferred state is rejected, uses conservative injection instead. | InitializationStability / convergence Improves initialization robustness at local locations where high-order transfer is inadmissible. | Keep enabled unless deliberately testing transfer rejection. | Full-multigrid initialization |
| Fine cleanup cyclesDefault: Robust 2; High-Speed 4; SST Wall-Bounded 3 | Extra fine-level cycles after coarse-to-fine initialization. | InitializationCost Reduces transfer/startup artifacts before normal solving. | Keep a small cleanup budget; increase if the fine level remains visibly under-converged. | Full-multigrid initialization |
| Turbulence cleanup cyclesDefault: Robust 0; High-Speed 0; SST Wall-Bounded 2 | Additional cleanup devoted to turbulent wall-bounded startup. | InitializationStability / convergenceCost Helps establish | Use the wall-bounded preset when needed rather than manually forcing large cleanup. | Full-multigrid initialization |
| Initialize with Full Multigrid | Runs the selected FMG initializer on a valid level-0 initial/loaded state. | InitializationCost Replaces/improves the initial solution field before the normal solve. | Use after boundary/material/physics setup is complete and the hierarchy has been validated. | Full-multigrid initialization |
Coarse Grid Viewer
Viewer controls are diagnostic only; they do not alter the simulation.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Viewer LevelDefault: 1 | Selects which retained hierarchy level is mapped back onto the original fine mesh for display. | Reporting / display Visualization only. | Use to inspect aggregate size/quality at each level. | Multigrid hierarchy |
| Display: Aggregate regions | Colors fine cells by their selected-level parent aggregate. | Reporting / display Display only. | Good first view of aggregate compactness and size. | Multigrid hierarchy |
| Display: Aggregate boundaries | Shows aggregate interfaces. | Reporting / display Display only. | Use to spot fragmented or irregular boundaries. | Multigrid hierarchy |
| Display: Coarse centroids and connectivity | Shows coarse centroids/connectivity over the fine mesh. | Reporting / display Display only. | Use to inspect coarse topology. | Multigrid hierarchy |
| Display: Cells per aggregate | Colors/labels by number of fine cells per aggregate. | Reporting / display Display only. | Check for severe size imbalance. | Multigrid hierarchy |
| Display: Worker partition | Displays parallel ownership/partition context. | Reporting / display Display only. | Use to relate hierarchy quality to partition boundaries. | Multigrid hierarchy |
| Display: Boundary classification | Displays coarse-boundary classifications. | Reporting / display Display only. | Use when boundary preservation is important to hierarchy quality. | Multigrid hierarchy |
| Highlight quality warningsDefault: On | Overlays warning-marked parent aggregates. | Reporting / display Display only; no solver change. | Keep enabled while qualifying a hierarchy. | Multigrid hierarchy |
| Show level | Displays the selected coarse-grid level using the current viewer mode. | Reporting / display Display only; it does not rebuild or modify the multigrid hierarchy. | Use after selecting a level/mode to inspect aggregate quality and boundary classification. | Multigrid hierarchy |
| Hide hierarchy | Removes the hierarchy overlay from the current visualization. | Reporting / display Display only; the hierarchy remains built and available to the solver. | Use to return to the normal solution view without rebuilding anything. | Multigrid hierarchy |
| Export VTU | Writes the selected hierarchy visualization data for external inspection. | Reporting / display No solution change. | Useful for design reviews and detailed mesh-quality analysis. | Multigrid hierarchy |
| Generate hierarchy audit... | Creates the detailed hierarchy-quality audit/report for the current built levels. | Reporting / display Reporting only; it does not change the active hierarchy or solution. | Use when warnings appear or before qualifying AggMG on a new mesh. | Multigrid hierarchy |
| Also export selected-level VTU audit fieldsDefault: Off | When hierarchy-audit generation is requested, also writes the selected level quality/audit fields into VTU output. | Reporting / display Reporting/export only; no solver effect. | Enable when you want to inspect warning metrics spatially in an external visualization tool. | Multigrid hierarchy |