Simulation Metadata#

The abacusnbody.metadata module contains the parameters and states for Abacus simulations like AbacusSummit. One can use this module to query information about simulations without actually downloading or opening any simulation files.

The main entry point to this module is the get_meta(simname, redshift=z) function. Examples and the API are below.

If one does have simulation files, it’s not necessary to use this module, and often it’s easier to use the metadata from the files directly because it’s automatically loaded via the Python API. For example, if using a CompaSO halo catalog, one can use cat.header to access metadata. However, a few header values, like the growth factor table and the linear power spectrum, are not present in the standard file headers. Applications that need those parameters should use this module.



import abacusnbody.metadata
meta = abacusnbody.metadata.get_meta('AbacusSummit_base_c000_ph000', redshift=0.1)
print(meta['OmegaNow_m'])  # Omega_M(z=0.1)
print(meta['OmegaNow_DE'])  # Omega_DE(z=0.1)

Growth Factors in AbacusSummit#

Growth factors in AbacusSummit are a bit of a special case, because the parameters actually contain a pre-computed table of \(D(z)\) for all the output epochs and the ICs. This table is a dict called GrowthTable. Since AbacusSummit input power spectra (i.e. CLASS power spectra) are generated at \(z=1\) (recorded under 'ZD_Pk_file_redshift'), one can compute the linear power spectrum at a different epoch via the ratio \(D(z)/D(1)\):

import abacusnbody.metadata
meta = abacusnbody.metadata.get_meta('AbacusSummit_base_c000_ph000')
Dz = meta['GrowthTable']
ztarget = 0.1
zpk = meta['ZD_Pk_file_redshift']  # 1.0
linear_pk = input_pk * (Dz[ztarget] / Dz[zpk])**2

Linear Power Spectrum#

The linear power spectrum generated by CLASS that is taken as input to the IC generator is stored in the metadata. For example, one can load the c000 CLASS power spectrum as follows, which corresponds to this power spectrum in the AbacusSummit repo: CLASS_power. The redshift of this power spectrum is specified by 'ZD_Pk_file_redshift' and is 1.0 for AbacusSummit.

import abacusnbody.metadata
meta = abacusnbody.metadata.get_meta('AbacusSummit_base_c000_ph000')
pk = meta['CLASS_power_spectrum']

Developer Details#

The metadata is stored in an ASDF file in the abacusnbody/metadata directory. The metadata files are built with scripts/metadata/, and then compressed with scripts/metadata/ (using compression on the pickled representation). Internally, the time-independent parameters are separated from the time-varying state values, but the two sets are combined into a single dict that is passed to the user.


Retrieve the cosmology and other code parameters associated with an Abacus simulation.

Each set of simulations, like AbacusSummit, has a corresponding repository of metadata. The simulation name will be used to infer which repository to look in.

abacusnbody.metadata.get_meta(simname, redshift=None)[source]#

Get the metadata associated with the given simulation.

  • simname (str) – The simulation name, like “AbacusSummit_base_ph000_c000”.

  • redshift (float or str) – The redshift


meta – The time-independent parameters and, if redshift is given, the time-dependent state values.

Return type: