Configuration¶

All settings for running DYNAMITE can be controlled from a single configuration file in yaml format. The basic structure of a yaml file are pairs of keys and values:

key : value


which can be organised into hierarchical levels separated by tabs:

main_key:
sub_key1 : value1
sub_key2 : value2


Comments are allowed, and begin with a #. Values can be any type of variable e.g. integers, floats, strings, booleans etc. DYNAMITE configuration files must have the following structure:

# Example DYNAMITE configuration file e.g. called config_file.yaml
---
###############################################################################
# SECTION 1 : SYSTEM
# Define the physical system i.e. the galaxy being modelled
###############################################################################

system_attributes:      # e.g. name, distance, ...
...

system_components:      # components of the system e.g. black hole, dark halo
component_1: ...
component_2: ...
...

system_parameters:      # extra parameters of the system
...

###############################################################################
# SECTION 2: SETTINGS
# Define other settings e.g. for the orbit library and weight solver
###############################################################################

orblib_settings:            # settings for the orbit library calculation
...

weight_solver_settings:     # settings for solving for orbital weights
...

parameter_space_settings:   # settings for parameter search
...

multiprocessing_settings:   # settings for multiprocessing
...

io_settings:                # settings for input/output locations
...

legacy_settings:            # location of Fortran programs
...


The following sections go through each section of the configuration file and enumerate all the options available for that section,

Examples of completed configuration files can be found in the tutorials, which you may like to use as templates for your own models.

Information about how the DYNAMITE configuration settings can be accessed, which may be useful for developers, can be found in the API documentation.

system_attributes¶

This section lists the following attributes of the system:

system_attributes:
distMPc: ...        # distance in MPc
name:  ...          # name for your galaxy
position_angle:     # in degrees


system_components¶

The system consists of a number of physical components - e.g. the stars, black hole, dark halo. For each component the following values must be specified

• component name: a descriptive name, but preferably short as this will be used to refer to the component in the code (e.g. bh for black hole)
• type: a string corresponding to one of the options in in component types

• contributes_to_potential: Boolean (not currently used)

• include: Boolean, whether to include this component or not. If False, equivalent to omitting this component entirely

• parameters. The required parameters for each component are listed in component types. Each parameter must have values specified for
• fixed: Boolean, whether the parameter is to be kept fixed

• value: an initial value for the parameter

• par_generator_settings: settings controlling parameter search (can be omitted if fixed=True). Note that if these settings are given, then value must be consistent with lo and hi.
• lo: minimum value

• hi: maximum value

• step: initial step size for parameter search

• minstep: minimum allowed stepsize for this parameter

• logarithmic: Boolean, whether logarithmic steps should be used for parameter search. If true, then (value, lo, hi) must all have log units.

• LaTeX: LaTeX string for this parameter to be used for plots.

component types¶

The following types of component are available, listed with their parameters:

• TriaxialVisibleComponent, a triaxial ellipsoid with surface density specified as an MGE,
• p: intrinsic axis ratio B/A (i.e. intermediate-to-major), where $$0<p<1$$

• q: intrinsic axis ratio C/A (i.e. minor-to-major), where $$0<q<p$$

• u: ratio between 2D observed and 3D intrinsic Gaussian widths of the MGE, i.e. $$\sigma_{2D}/\sigma_{3D}$$

• additionally, you must specify observed data for this component

• Plummer
• a: scale length [arcsec]

• m: mass [$$M_\odot$$]

• NFW
• c: concentration parameter [$$R_{200}$$ / NFW-scale-length]

• f: dark matter fraction [$$M_{200}$$ / total-stellar-mass]

• NFW_m200_c, an NFW halo with mass-concentration from Dutton & Maccio (2014)
• f: dark matter fraction [$$M_{200}$$ / total-stellar-mass]

• Hernquist
• rhoc: central density [$$M_\odot/\mathrm{km}^3$$]

• rc: scale length [km]

• TriaxialCoredLogPotential, see e.g. Binney & Tremaine second edition p.171
• p: intrinsic intermediate-to-major axis ratio, where $$0<p<1$$

• q: intrinsic minor-to-major axis ratio, where $$0<q<p$$

• Rc: core radius [kpc]

• Vc: circular velocity for $$r>>R_c$$ [km/s]

• GeneralisedNFW from Zhao (1996)
• c: concentration parameter [$$R_{200}$$ / NFW-scale-length]

• Mvir: virial mass $$M_{200}$$ [$$M_\odot$$]

• gam: AKA gamma, the inner logarithmic density slope, must be $$\leq 1$$

Note

currently, there is only one combination of component types that is valid. This is to ensure compatibility with the Fortran implementation of the orbit integrator. Later implementations may offer more flexibility. The only current valid combination of components is:

• one Plummer component
• representing the black hole

• the scale length a should be fixed to some arbitrarily small value

• one TriaxialVisibleComponent component
• representing the stars

• exactly one out of [NFW, NFW_m200_c, Hernquist, TriaxialCoredLogPotential, GeneralisedNFW]
• representing the dark halo

observed data¶

The TriaxialVisibleComponent represents the galaxy’s stars, and therefore has associated observations. You must specify the following entries with filenames for observed data:

• TriaxialVisibleComponent
• mge_lum: string, filename for the MGE of the projected luminosity density, with intensity units of $$L_\odot \mathrm{pc}^{-2}$$.

• mge_pot: string, filename for the MGE of the projected mass density, with intensity units of $$M_\odot \mathrm{pc}^{-2}$$. If you assume that stellar-mass follows stellar-light, then the files mge_lum and mge_pot will be identical.

• kinematics
• name of the kinematic set: a descriptive name, best without spaces as it will be part of the kinematic plot file name.
• type: type of kinematics - either GaussHermite or BayesLOSVD

• weight: float, weighting applied to this kinematic set in chi2 calculation

• datafile: string, filename for the kinematics ECSV data file

• aperturefile: string, filename of the aperture file for this kinematic set

• binfile: string, filename of the bin file for this kinematic set

• hist_width: optional, float or ‘default’, the width (i.e. min. to max. value) of the velocity histogram for storing orbits. The default option is a width slightly wider than that of the observed kinematics.

• hist_center: optional, float or ‘default’, the center of the velocity histogram for storing orbits. The default option is 0.

• hist_bins: optional, int or ‘default’, the number of bins in the velocity histogram for storing orbits. The default option gives about 10 times better velocity sampling than the data.

system_parameters¶

This section is used for global parameters of the system i.e. those which are unrelated to any particular component.

Currently there is only one such parameter, ml, which is a scale factor for the total mass of the system. Note that this scales the mass of every component of the system i.e. not just the stellar component (despite the acronym ml resembling mass-to-light). This is a time-saving trick: by scaling the total mass of the system, we are able to cheaply re-use orbit-libraries by re-scaling their velocity axes.

Care must be taken when interpreting mass parameters for models with different ml. For example, say the system has a GeneralisedNFW component with Mvir=100 but the system’s ml parameter is equal to 2. The GeneralisedNFW would therefore actually represent a halo with mass Mvir=200. Further note that the NFW component is parameterised with a mass fraction f rather than an absolute mass, and this fraction does not need to be re-scaled by ml.

Specifying the ml parameter in the configuration file follows the same pattern as other parameters,

• system_parameters
• ml
• fixed: Boolean, whether ml is to be kept fixed

• value: an initial value for ml

• par_generator_settings: settings controlling parameter search (can be omitted if fixed=True). Note that if these settings are given, then value must be consistent with lo and hi.
• lo: minimum value

• hi: maximum value

• step: initial step size for parameter search

• minstep: minimum allowed stepsize for this parameter

• logarithmic: Boolean, whether logarithmic steps should be used for parameter search. If true, then (value, lo, hi) must all have log units

• LaTeX: LaTeX format string for this parameter to be used for plots, e.g. in axis labels.

orblib_settings¶

This section is used for settings relevant for the calculation of orbit libraries.

Note

The size of the orbit library is controlled by 4 parameters: $$(n_E, n_{I2}, n_{I3})$$ and dithering. The parameters $$(n_E, n_{I2}, n_{I3})$$ are the grid-dimensions in the three integrals-of-motion used for generating orbit initial conditions. Each initial-condition is used three times: once to seed a box-orbit, and twice to seed tube-orbits with opposing senses of rotation. The parameter dithering then seeds a mini-grid of orbits around each set of initial conditions, of size dithering$$^3$$. The total number of orbits in the library is thus

$\text{total number of orbits} = 3 \; n_E \; n_{I2} \; n_{I3} \; \mathrm{(dithering)}^3$
• orblib_settings
• nE: integer, size of grid in integral-of-motion $$E$$

• nI2: integer, size of grid in second integral-of-motion $$I_2$$ (similar to $$L_z$$). Must be at least 4.

• nI3: integer, size of grid in third integral-of-motion $$I_3$$

• logrmin: log10 of minimum orbit radius in arcsecs

• logrmax: log10 of maximum orbit radius in arcsecs

• random_seed: integer, used for stochastically blurring orbit library by the PSF. Any value $$\leq 0$$ gives a stochastic seed.

The following settings must also be set in the configuration files but have typical values which should generally be sufficient and should not be changed,

• orblib_settings
• orbital_periods: integer, typical 200, the number of orbital periods to integrate orbits

• sampling: integer, typical 50000, number of points to sample for each orbit in the meridional plane

• starting_orbit: integer, typically 1, the index of which orbit to start integrating orbits

• number_orbits: integer, the number of orbits to integrate, if -1 then integrate all orbits

• accuracy: typical 1.0d-5, the accuracy of the orbit integrator

There is also an optional setting,

• orblib_settings
• use_new_mirroring: boolean

This controls whether or not to use the correction to orbit mirroring introduces in Quenneville et al 2021 . This is optional: if ommited, the default is True.

weight_solver_settings¶

Settings relevant for solving for orbital weights.

Note

If any kinematic set has type BayesLOSVD, then the weight_solver_settings must have type NNLS

• weight_solver_settings
• type: string, one of LegacyWeightSolver to use Fortran implementations of Lawson and Hanson non-negative least-squares algorithm, or NNLS to use Python implementations

• nnls_solver: options depend on the type selected. If
• type = LegacyWeightSolver then set nnls_solver : 1

• type = NNLS then nnls_solver can be one of the strings,
• lum_intr_rel_err: float, typical 0.01, the systematic error (fraction) applied to the intrinsic luminosity constraint

• sb_proj_rel_err: float, typical 0.01, the systematic error (fraction) applied to the projected surface brightness constraint

• CRcut: Boolean, default False, whether to use the CRcut solution for the counter-rotating orbit problem. See Zhu et al. 2018 for more details.

If any kinematics have of type GaussHermite , then the following additional settings are needed.

• weight_solver_settings
• number_GH: integer, the number of Gauss-Hermites

• GH_sys_err: a string of length 2 + number_GH floats, the systematic error applied to V, sigma, h3, …, hN

If any kinematic set has type BayesLOSVD, then the weight_solver_settings must have type NNLS, and no additional settings are required.

If DYNAMITE shall recover from an unsuccessful weight solving attempt, the following option can be used:

• weight_solver_settings
• reattempt_failures: if True, DYNAMITE will use a model’s existing orblibs from an earlier run to reattempt weight solving.

parameter_space_settings¶

Settings relevant for parameter search.

• parameter_space_settings
• generator_type: string, specifying which algorithm to use for parameter search. Note that all generator types will exclude invalid or already-executed parameter combinations by default. The different options are:
• GridWalk: Start at the initial point. Start the iteration: (i) find the model with the minimum $$\chi^2$$, (ii) for each free parameter, seed new models by independently take a step $$\pm 1$$ of size step (cartesian grid in one step size, so if 2 parameters are free, 8 new models will be created). Repeat until $$\chi^2$$ is improved by less than min_delta_chi2. This may result in a large number of models.

• LegacyGridSearch: Start at the initial point. Start the iteration: (i) find all models with $$|\chi^2 - \chi_\mathrm{min}^2|$$ within the threshold (specified with threshold_del_chi2_XXX), (ii) for each model within the threshold, seed new models by independently take a step $$\pm 1$$ of size step (i.e. as done for GridWalk). If no new models are seeded at the end of an iteration, then divide all parameter stepsizes by two till their specified minstep are reached.

• FullGrid: Create a full grid, i.e. a Cartesian grid in all free parameters, with bounds lo/hi and stepsize step. Warning: If several (>3) parameters are free, this will result in a large number of models.

• which_chi2: string, specifies which $$\chi^2$$ value to consider when generating new parameters, must be one of the following:
• kinchi2: this includes contributions from only the kinematics. If GaussHermite kinematics are used then this is includes terms from all Hermite coefficients $$h_1, h2, h3, ..., h_N$$. If BayesLOSVD kinematics are used, then this includes contributions from all LOSVD bins.

• chi2: this includes contributions from the observed surface density, de-projected 3D density, and kinematics (as specified above).

• generator_settings: if generator_type = LegacyGridSearch, then one of the following two settings must be set. These are the $$|\chi^2|$$ thresholds used for in LegacyGridSearch,
• threshold_del_chi2_abs: an absolute $$|\chi^2|$$ threshold

• threshold_del_chi2_as_frac_of_sqrt2nobs: a threshold given as a fraction of $$\sqrt{2N_\mathrm{obs}}$$ where $$N_\mathrm{obs}$$ is the total number of kinematic observations, which is equal to the number of spatial apertures multiplied by (i) number_GH if GaussHermite kinematics are used, or (ii) the number of LOSVD bins if BayesLOSVD kinematics are used.

• stopping_criteria: all of the following must be specified. If any of the criteria are met, then the parameter generation will stop:
• One of min_delta_chi2_abs or min_delta_chi2_rel must be set: float, absolute or relative tolerance for ending the parameter search. If an iteration does not improve the minimum chi2 by this threshold, no new iteration will be performed.

• n_max_mods: int, maximum number of models desired

• n_max_iter: int, maximum number of iterations desired

io_settings¶

Settings specifying the location of input and output directory names. Paths are relative to the current working directory, and can be given with or without trailing slash:

io_settings
input_directory: "input_files/"     # directory holding input data
output_directory: "output/"         # directory (will be created) for output
all_models_file: "all_models.ecsv"  # filename for the summary file of models run so far


multiprocessing_settings¶

Settings for multiprocessing. Models can be evaluated in parallel, with the number of parallel processes specified by the ncpus* settings:

multiprocessing_settings:
ncpus: 4                              # integer or string 'all_available' (default: 'all_available')
ncpus_weights: 4                      # int or 'all_available', optional (default: ncpus), not used by all iterators
orblibs_in_parallel: True             # calculate tube and box orbits in parallel (default: True)
modeliterator: 'SplitModelIterator'   # optional (default: 'ModelInnerIterator')


Due to very different CPU and memory consumption of orbit integration and weight solving, there are two different settings: while orbit integration will use ncpus, weight solving will use ncpus_weights parallel processes. Note that ncpus_weights will default to ncpus if not specified. Currently, only the SplitModelIterator model iterator and recovering from an unsuccessful weight solving attempt (reattempt_failures=True) use the ncpus_weights setting.

If ncpus : 'all_available' or ncpus_weights : 'all_available' is set, then DYNAMITE automatically detects the number of available cpus for parallelisation.

legacy_settings¶

Location of the legacy Fortran programs:

legacy_settings:
directory: "default"  # or an alternative directory


If default, then the Fortran programs created during installation are used. Can be set to an alternative directory if required.