Multi-grid

Generated from SU2 commit 6b54b78464 on 2026-10-23. Do not edit this page. Edit the comment above the option in Common/src/CConfig.cpp instead.

MGLEVEL

Multi-grid Levels. DEFAULT: 0

More in config_template.cfg: Max. number of multi-grid levels (0 = no multi-grid)

MGCYCLE

Multi-grid cycle. OPTIONS: See MG_Cycle_Map. Defualt V_CYCLE

More in config_template.cfg: Multi-grid cycle (V_CYCLE, W_CYCLE, FULLMG_CYCLE)

MG_PRE_SMOOTH

Multi-grid pre-smoothing level

More in config_template.cfg: Max. iterations for multi-grid pre-smoothing level

MG_POST_SMOOTH

Multi-grid post-smoothing level

More in config_template.cfg: Max. iterations for multi-grid post-smoothing level

MG_CORRECTION_SMOOTH

Jacobi implicit smoothing of the correction

MG_DAMP_RESTRICTION

Damping factor for the residual restriction. DEFAULT: 0.75

MG_DAMP_PROLONGATION

Damping factor for the correction prolongation. DEFAULT 0.75

MG_SMOOTH_EARLY_EXIT

Enable early exit for MG smoothing when RMS drops below threshold. DEFAULT: NO

More in config_template.cfg: Enable early exit from multigrid smoothing when the residual RMS drops below MG_SMOOTH_RES_THRESHOLD * initial_rms (NO, YES)

MG_SMOOTH_RES_THRESHOLD

Early exit smoothing when current_rms drops below threshold * initial_rms. DEFAULT: 0.9

More in config_template.cfg: Relative RMS reduction threshold for the multigrid smoothing early exit. Smoothing stops when current_rms < threshold * initial_rms (default 0.5)

MG_SMOOTH_OUTPUT

Print compact per-cycle smoothing iteration summary. DEFAULT: NO

More in config_template.cfg: Print a compact per-cycle summary of smoothing iterations and residuals (NO, YES)

MG_SMOOTH_STAGNATION_TOL

Stop smoothing if current_rms >= previous_rms this value. Values < 1.0 enable early exit on stagnation, 1.0 only exits on defect growth. DEFAULT: 0.99

More in config_template.cfg: Stop smoothing when current_rms >= previous_rms * this value. Values below 1.0 exit early on stagnation, 1.0 exits only when the defect grows, 0 disables the check (default 0.99)

  • Type: real number
  • Default: 0.99
  • In config_template.cfg: MG_SMOOTH_STAGNATION_TOL= 0.99
  • Code: CConfig.cpp line 2103

MG_SMOOTH_COEFF

Smoothing coefficient for the correction prolongation Jacobi smoother. DEFAULT: 1.25

More in config_template.cfg: Smoothing coefficient for the Jacobi correction-prolongation smoother (default 1.25)

MG_MIN_MESHSIZE

Minimum number of CVs on the coarsest multigrid level, counted over the whole level rather than per rank, so the hierarchy does not change with the number of ranks. DEFAULT: 500

More in config_template.cfg: Minimum number of control volumes on the coarsest multigrid level, counted over the whole level rather than per rank, so the hierarchy does not change with the number of MPI ranks. A level holding fewer control volumes than this is not created.

MG_IMPLICIT_LINES

Pave the coarse grid with advancing fronts raised from boundaries that carry a stretched layer normal to themselves. DEFAULT: NO

More in config_template.cfg: Pave the coarse grid with advancing fronts raised from boundaries that carry a stretched layer normal to themselves (NO, YES)

MG_STARTUP_ITER

Max number of iterations spent on each mesh during the Full Multigrid (FMG) startup phase. DEFAULT: 100

More in config_template.cfg: Number of iterations spent on each mesh during the Full Multigrid (FMG) startup phase. After this many iterations the solution is prolongated to the next finer mesh. It is also the length of the CFL ramp every level is brought up over, the finest grid included, which is what keeps the CFL from jumping when the startup hands the solution over. 0 removes the iteration budget, leaving MG_STARTUP_CONVERGENCE and MG_STARTUP_STAGNATION to decide, and disables the ramp (default 100).

MG_STARTUP_CONVERGENCE

During the startup phase of Full-MG, leave the current level once CONV_FIELD has dropped by this many orders of magnitude relative to its value when the level became active. DEFAULT: -2

More in config_template.cfg: Full-MG promotion on convergence: orders of magnitude (log10) that CONV_FIELD must drop on the active level, relative to its value when that level became active, before promoting to the next finer level early. Negative for a drop, on the same scale as CONV_RESIDUAL_MINVAL, so -2 asks for a fall to 1% of the starting residual. Only residual convergence fields are used. Make it more negative to demand a deeper drop; a large negative value effectively disables this criterion (default -2).

MG_STARTUP_STAGNATION

Full-MG promotion on stagnation. If the active level’s residual ratio between successive iterations exceeds this value for MG_STARTUP_STAGNATION_ITER consecutive iterations, promote to the next finer level without waiting out MG_STARTUP_ITER. 0 disables it. DEFAULT: 0.99

More in config_template.cfg: Full-MG promotion on stagnation: if the active level’s residual ratio between successive iterations exceeds this for MG_STARTUP_STAGNATION_ITER consecutive iterations, promote to the next finer level early. 0 disables (default 0.99).

MG_STARTUP_STAGNATION_ITER

Consecutive stalled iterations required before Full-MG promotes on stagnation. 0 disables it, as MG_STARTUP_STAGNATION= 0 does. DEFAULT: 5

More in config_template.cfg: Consecutive stalled iterations required before Full-MG promotes on stagnation. 0 disables the criterion, as MG_STARTUP_STAGNATION= 0 does (default 5).

  • Type: integer
  • Default: 5
  • In config_template.cfg: MG_STARTUP_STAGNATION_ITER= 5
  • Code: CConfig.cpp line 2125

MG_CFL_SCALING

Per-level CFL scaling factors for coarse MG levels. Entry i is the ratio CFL(i+1)/CFL(i). If fewer values than nMGLevels are given, the last value is repeated. DEFAULT: 0.25 (i.e., 1/4 per level)

More in config_template.cfg: Per-level CFL scaling factors for the coarse multigrid levels. Entry i is the ratio CFL(i+1)/CFL(i). If fewer values than MGLEVEL are given the last one is repeated (default 0.25, i.e. a quarter of the CFL per level)

  • Type: list of real numbers
  • In config_template.cfg: MG_CFL_SCALING= ( 0.25 )
  • Code: CConfig.cpp line 2128


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