Poisson Parameters

This namelist, &POISSON_PARAMS, is used to specify runtime parameters for the Poisson solver. It is used only if poisson=.true. or pic=.true.

Two different Poisson solvers are available in RAMSES: conjugate gradient (CG) and multigrid (MG). Unlike the CG solver, MG has an initialization overhead cost (at every call of the solver), but is much more efficient on very big levels with few “holes”. The multigrid solver is therefore used for all coarse levels.

In addition, MG can be used on refined levels in conjuction with CG. The parameter cg_levelmin selects the Poisson solver as follows:

• Coarse levels are solved with MG

• Refined levels with l < cg_levelmin are solved with MG

• Refined levels with l >= cg_levelmin are solved with CG

Variable name	Fortran type	Default value	Description
gravity_type	int	0	Type of gravity force. Possible choices are: gravity_type=0 self-gravity (Poisson solver); gravity_type>0 analytical gravity vector; gravity_type<0 self-gravity plus additional analytical density profile
epsilon	real	1e-4	Stopping criterion for the iterative Poisson solver: residual 2-norm should be lower than epsilon times the right hand side 2-norm.
gravity_params	real array	0.0,	Parameters used to define the analytical gravity field (routine gravana.f90) or the analytical mass density field (routine rho_ana.f90).
cg_levelmin	integer	999	Minimum level from which the Conjugate Gradient solver is used in place of the Multigrid solver.
cic_levelmax	integer	0	Maximum level for CIC dark matter interpolation (default cic_levelmax=nlevelmax)