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.

Solvers

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

Gravity types

Different sources of gravity can be added to the simulation. To activate self-gravity of the gas and particles, set self_gravity=.true.. Additional sources of gravity can be added by

• adding an analytical density distribution to the Poisson source term from which the gravitational potential is determined (see rho_ana.f90)

• adding an analytical force directly (see gravana.f90)

These two methods can be combined by setting both gravity_rho_ana_type and gravity_force_ana_type.

Variable name	Fortran type	Default value	Description
gravity_type	integer	0	(deprecated) 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
self_gravity	logical	.true.	Switch on self-gravity (Poisson solver)
gravity_rho_ana_type	integer	0	Add gravity from an analytical density profile. This will add an analytical contribution to the Poisson source term. 0 = no additional contribution, 2 = a point mass, 3 = galactic disk (see rho_ana.f90)
gravity_force_ana_type	integer	0	Add an analytical gravitational force. 0 = no additional contribution, 1 = constant vector, 2 = a point mass, 3 = galactic disk (see gravana.f90)
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,	(deprecated) Parameters used to define the analytical gravity field (routine gravana.f90) or the analytical mass density field (routine rho_ana.f90).
gravity_rho_ana_params	real array	0.0,	Parameters used to define the analytical mass density field (routine rho_ana.f90).
gravity_force_ana_params	real array	0.0,	Parameters used to define the analytical gravity field (routine gravana.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)