Multigrid solvers

The following inputs can be set directly in the AMReX solver classes but we set them via the MFIX-Exa routines because we may want different inputs for the different solvers called by MFIX-Exa.

Nodal projection

NOTE: the nodal solver settings are read in directly by AMReX, the MAC and diffusion settings by MFIX-Exa.

These control the nodal projection and must be preceded by “nodal_proj.”:

	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 allowin 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

These control the MAC projection and must be preceded by “mac_proj.”:

	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

NOTE: If the nodal_proj and mac_proj hypre_namespace’s are set, they must be distinct unless set to hypre, in which case the default behavior is recovered in which case hypre settings apply to all solvers.

Diffusion

These control the diffusion solver and must be preceded by “diffusion.”:

	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

The following inputs control the hypre settings and are read directly by AMReX when we use hypre as the bottom solver, i.e., when nodal_proj.bottom_solver = hypre and/or when mac_proj.bottom_solver = hypre (see Multigrid solvers) These settings must be preceded by the hypre_namespace setting corresponding to the solver (see Multigrid solvers).

NOTE: By default, the MAC and nodal projections use the same settings specified with the namespace hypre, however the solvers can be configured separately by specifying mac_proj.hypre_namespace and nodal_proj.hypre_namespace.

When not using the default namespace hypre, additional restrictions apply:

1. Both mac_proj.hypre_namespace and nodal_proj.hypre_namespace must be set.

2. mac_proj.hypre_namespace and nodal_proj.hypre_namespace must be unique.

	Description	Type	Default
verbose	Verbosity of hypre	Int	0
adjust_singular_matrix	Should be true if the problem to be solved has singular matrix	Bool	false
hypre_solver	Type of hypre solver Options are BoomerAMG, GMRES, COGMRES, LGMRES, FlexGMRES, BiCGSTAB, PCG or Hybrid	String	BoomerAMG
hypre_preconditioner	Type of preconditioner Options are BoomerAMG or euclid	String	none
recompute_preconditioner	Recompute preconditioner during runs	Bool	true
write_matrix_files	Write out matrix into text files	Bool	false
overwrite_existing_matrix_files	Over-write existing matrix files	Bool	false
bamg_verbose	Verbosity of BoomerAMG preconditioner	Int	0
bamg_logging	When using BoomerAMG preconditioner See HYPRE_BoomerAMGSetLogging	Int	0
bamg_coarsen_type	When using BoomerAMG preconditioner See HYPRE_BoomerAMGSetCoarsenType	Int	6
bamg_cycle_type	When using BoomerAMG preconditioner See HYPRE_BoomerAMGSetCycleType	Int	1
bamg_relax_type	When using BoomerAMG preconditioner See HYPRE_BoomerAMGSetRelaxType	Int	6
bamg_relax_order	When using BoomerAMG preconditioner See HYPRE_BoomerAMGSetRelaxOrder	Int	1
bamg_num_sweeps	When using BoomerAMG preconditioner See HYPRE_BoomerAMGSetNumSweeps	Int	2
bamg_max_levels	When using BoomerAMG preconditioner See HYPRE_BoomerAMGSetMaxLevels	Int	20
bamg_strong_threshold	When using BoomerAMG preconditioner See HYPRE_BoomerAMGSetStrongThreshold	Real	0.57
bamg_interp_type	When using BoomerAMG preconditioner HYPRE_BoomerAMGSetInterpType	Int	0