Multigrid solvers

Nodal projection

The following inputs are defined using the nodal_proj prefix.

	Description	Type	Default
verbose	Verbosity of multigrid solver in nodal projection	Int	0
bottom_verbose	Verbosity of BiCGStab solver in nodal projection	Int	0
mg_rtol	Relative tolerance in nodal projection	Real	1.e-11
mg_atol	Absolute tolerance in nodal projection	Real	1.e-14
maxiter	Maximum number of iterations in the nodal projection	Int	100
bottom_maxiter	Maximum number of iterations in the nodal projection bottom solver if using bicg, cg, bicgcg or cgbicg	Int	100
mg_max_coarsening_level	Maximum number of coarser levels to allow in the nodal projection If set to 0, the bottom solver will be called at the current level	Int	100
bottom_solver	Which bottom solver to use in the nodal projection Options are bicgcg, bicgstab, cg, cgbicg, smoother or hypre	String	bicgcg
hypre_namespace	Namespace to use in the nodal projection when using hypre to control hypre specific settings. It can be any string.	String	hypre
hypre_interface	Which interface to use in the nodal projection when using hypre Options are ij, semi_structured or structured	String	ij

MAC projection

The following inputs are defined using the mac_proj prefix.

	Description	Type	Default
verbose	Verbosity of multigrid solver in MAC projection	Int	0
bottom_verbose	Verbosity of BiCGStab solver in MAC projection	Int	0
mg_rtol	Relative tolerance in MAC projection	Real	1.e-11
mg_atol	Absolute tolerance in MAC projection	Real	1.e-14
maxiter	Maximum number of iterations in the MAC projection	Int	200
bottom_maxiter	Maximum number of iterations in the MAC projection bottom solver if using bicg, cg, bicgcg or cgbicg	Int	200
mg_max_coarsening_level	Maximum number of coarser levels to allow in the MAC projection If set to 0, the bottom solver will be called at the current level	Int	100
bottom_solver	Which bottom solver to use in the MAC projection Options are bicgcg, bicgstab, cg, cgbicg, smoother or hypre	String	bicgcg
hypre_namespace	Namespace to use in the MAC projection when using hypre to control hypre specific settings. It can be any string.	String	hypre
hypre_interface	Which interface to use in the MAC projection when using hypre Options are ij, semi_structured or structured	String	ij

Diffusion

The following inputs are defined using the diffusion prefix.

	Description	Type	Default
verbose	Verbosity of linear solver for diffusion solve	int	0
bottom_verbose	Verbosity of BiCGStab solver in diffusion solve	int	0
mg_rtol	Relative tolerance in diffusion solve	Real	1.e-11
mg_atol	Absolute tolerance in diffusion solve	Real	1.e-14
maxiter	Maximum number of iterations in diffusion solve	int	100
bottom_maxiter	Maximum number of iterations in diffusion solve bottom solver if using bicg, cg, bicgcg or cgbicg	int	100
mg_max_coarsening_level	Maximum number of coarser levels to allow in diffusion solve If set to 0, the bottom solver will be called at the current level	int	100
bottom_solver	Which bottom solver to use in the diffusion solve Options are bicgcg, bicgstab, cg, cgbicg, or smoother	string	bicgcg

Hypre Settings

hypre settings are specified using the following inputs which are read directly by AMReX when hypre is used as the bottom solve for the MAC and/or nodal projections. By default, these inputs are defined using the hypre prefix, however different settings for the nodal and MAC projections can be used by specifying a hpyre_namespace for each solver.

Warning

• MFIX-Exa must be built with hypre enabled to use hypre as the bottom solve.

• If hypre is used for the nodal and MAC projections, then either the hypre_namespace must be left as the default (hypre) or unique name spaces must be provided for both.

These inputs follow the typical approach for using hypre in MFIX-Exa where BoomerAMG is employed as a preconditioner and GMRES for the linear solver.

	Description	Type	Default
hypre_preconditioner	Type of preconditioner Options are BoomerAMG or euclid	string	none
recompute_preconditioner	Recompute preconditioner during runs	Bool	true
hypre_solver	Type of hypre solver Options are BoomerAMG, GMRES, COGMRES, LGMRES, FlexGMRES, BiCGSTAB, PCG or Hybrid	string	BoomerAMG
verbose	Verbosity of hypre	int	0
num_krylov	Number of iterations	int	50

The following inputs are valid when using BoomerAMG as a preconditioner or solver.

	Description	Type	Default
bamg_verbose	Set BoomerAMG verbosity	int	0
bamg_logging	See HYPRE_BoomerAMGSetLogging	int	0
bamg_max_iterations	See HYPRE_BoomerAMGSetMaxIter	int	1
bamg_precond_tolerance	See HYPRE_BoomerAMGSetTol	Real	0.0
bamg_coarsen_type	See HYPRE_BoomerAMGSetCoarsenType	int	6
bamg_cycle_type	See HYPRE_BoomerAMGSetCycleType	int	1
bamg_relax_order	See HYPRE_BoomerAMGSetRelaxOrder	int	1
bamg_relax_type	See HYPRE_BoomerAMGSetRelaxType	int	6
bamg_down_relax_type	See HYPRE_BoomerAMGSetCycleRelaxType	int	11
bamg_up_relax_type	See HYPRE_BoomerAMGSetCycleRelaxType	int	11
bamg_coarse_relax_type	See HYPRE_BoomerAMGSetCycleRelaxType	int	11
bamg_num_sweeps	See HYPRE_BoomerAMGSetNumSweeps	int	2
bamg_num_down_sweeps	See HYPRE_BoomerAMGSetCycleNumSweeps	int	2
bamg_num_up_sweeps	See HYPRE_BoomerAMGSetCycleNumSweeps	int	2
bamg_num_coarse_sweeps	See HYPRE_BoomerAMGSetCycleNumSweeps	int	1
bamg_max_levels	See HYPRE_BoomerAMGSetMaxLevels	int	20
bamg_strong_threshold	See HYPRE_BoomerAMGSetStrongThreshold	Real	0.57
bamg_interp_type	See HYPRE_BoomerAMGSetInterpType	int	0
bamg_variant	See HYPRE_BoomerAMGSetVariant	int	0
bamg_keep_transpose	See HYPRE_BoomerAMGSetKeepTranspose	int	0
bamg_min_coarse_size	See HYPRE_BoomerAMGSetMinCoarseSize	int	1
bamg_max_coarse_size	See HYPRE_BoomerAMGSetMaxCoarseSize	int	9
bamg_pmax_elmts	See HYPRE_BoomerAMGSetPMaxElmts	int	4
bamg_agg_num_levels	See HYPRE_BoomerAMGSetAggNumLevels	int	0
bamg_agg_interp_type	See HYPRE_BoomerAMGSetAggInterpType	int	4
bamg_agg_pmax_elmts	See HYPRE_BoomerAMGSetAggPMaxElmts	int	0
bamg_trunc_factor	See HYPRE_BoomerAMGSetTruncFactor	Real	0.1
bamg_set_restriction	See HYPRE_BoomerAMGSetRestriction	int	0

	Description	Type	Default
adjust_singular_matrix	Should be true if the problem to be solved has singular matrix	Bool	false
overwrite_existing_matrix_files	Over-write existing matrix files	Bool	false

Note

This list is likely incomplete because the AMReX / hypre interface continues to evolve.