The Config File

General structure

The MUSIC configuration file is organized into sections, whose names appear in square brackets and options, which are assigned a value with the equal '=' operator. Currently, the following sections exist:

Section Tag	Description
[setup]	General setup for the simulation box and the refinement hierarchy as well as code behaviour control
[cosmology]	Cosmological parameters and the transfer function are defined here
[random]	The random seeds and the behaviour of the random number generator
[output]	The ouput plug-in is selected and parameters for output
[poisson]	Behaviour of the multi-grid Poisson solver is controlled

The [setup] section

General setup for the simulation box and the refinement hierarchy as well as code behavior control is defined using the options available in this section. There is support for various region specifications via plug-ins that can be selected via the region parameter. Currently, MUSIC implements two region generator plugins that will be described below.

Parameter	Description	Value Type
boxlength	The size of the full simulation box in comoving Mpc/h	real
zstart	The starting redshift for the simulation	real
region	The method used to generate the refinement hierarchy. Currently the methods box and ellipsoid are supported. If this parameter is not specified, it defaults to box.	string
levelmin	The level of the coarse grid which covers the full simulation box. The number specified is the 2-log of the number of grid cells per dimension, e.g. a level of 7 corresponds to 27=128 cells/dimension.	int
levelmax	The maximum refinement level in the simulation. This value has to be larger or equal to levelmin. This sets the effective resolution in the refinement region to 2levelmax cells/dimension	int
levelmin_TF	The level of the coarse grid when the density grid is computed (the convolution with the transfer function is performed). This can be set to a number larger than levelmin, the density field will be averaged down after the convolution has been performed and the Poisson solver is invoked. Essentially, this improves the accuracy of the coarser density modes when a low resolution in the coarsest level is desired in the final simulation.	int
force_equal_extent	Forces the refinement region to be a cube with edge length equal to the largest length determined from the region parameters.	bool
padding	Number of grid cells in intermediate levels (when using levelmax>levelmin+1) surrounding the nested grids. The extent of an intermediate level is N/2+2*padding if N is the number of cells in the next finer level.	int
blocking_factor	This parameter can be used to require the dimensions of initial grids to be multiples of blocking_factor. Not used if parameter is not present. This is mainly necessary to optimize for block based AMR.	int
align_top	Require subgrids to be always aligned with the coarsest grid? This is necessary for some codes (ENZO) but not for others (Gadget).	bool
baryons	Set to yes if also initial conditions for baryons shall be generated	bool
use_2LPT	Set to yes if 2nd order Lagrangian perturbation theory shall be used to compute particle displacements and velocities	bool

Region box (default)

The default region generator is the cuboid ‘box’ region, specified by giving the coordinates of the bounding box of the high-resolution region.

Parameter	Description	Value Type
ref_offset	Offset of the refinement region. Given as three comma-separated real values in units of the box length, e.g. 0.3, 0.4, 0.14 . You can only specify ref_offset or ref_center, not both.	3*real
ref_center	Center of the refinement region. Given as three comma-separated real values in units of the box length, e.g. 0.3, 0.4, 0.14.  You can only specify ref_offset or ref_center, not both.	3*real
ref_extent	Extent of the refinement region. Given as three comma-separated real values in units of the box length, e.g. 0.3, 0.4, 0.14  You can only specify ref_extent or ref_dims, not both.	3*real
ref_dims	Instead of ref_extent, also the resolution of the high resolution region in grid cells can be specified directly.  You can only specify ref_extent or ref_dims, not both.	3*int

Region ellipsoid

Instead of the default cuboid regions, a set of points can be specified that define the high-resolution region. When using ellipsoid, a minimum volume bounding ellipsoid will be fit to these points. For particle codes, only high-resolution particles in this region will be written out, for grid codes, masks will be written out that reflect the shape of the ellipsoid.

Parameter	Description	Value Type
region_point_file	ASCII file containing point coordinates of the particles in the Lagrangian patch of the region of interest. These need to be given in box coordinates, i.e. [0..1], one point per line.	3*real
region_point_shift	[optional] If the simulation from which the coordinates in region_point_file have been determined was already a zoom simulation, the coordinates in the IC file need to be shifted back to their original position (the zoom region had been centered). Specify here the shift that was applied in the centering of the zoom region, as has been output by MUSIC in the line, e.g.  - Domain will be shifted by (-12, -12, -12) If you specify the shift, also the levelmin of that simulation needs to be specified as below:	3*int
region_point_levelmin	[optional, but req. if region_point_shift is specified] The levelmin of the zoom-in simulation that has been run to determine the points that determine the region.	3*real

Region convex_hull

TBD