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name: cosmology description: "Use Astropy cosmology realizations, FLRW classes, distances, ages, redshift inversion, cosmology units, equivalencies, and serialization." metadata: disco-role: operating disable-model-invocation: true license: BSD 3-Clause

Cosmology Router

Use this sub-skill when a task centers on astropy.cosmology models, realizations, cosmological calculations, redshift inversion, or cosmology I/O.

Load This When

• The task mentions Planck18, default_cosmology, FlatLambdaCDM, LambdaCDM, w0waCDM, cosmology parameters, or cloning a cosmology.
• The user needs age, lookback time, comoving/luminosity/angular-diameter distance, distance modulus, Hubble parameter, density parameters, critical density, or absorption distance.
• The task uses z_at_value, vectorized redshifts, cosmology units, little-h equivalencies, or cosmology serialization.
• A workflow must preserve cosmology metadata in mappings, tables, YAML, ECSV, or another registered format.

Route Away When

• General units/equivalencies are the main question; use ../units-constants/SKILL.md.
• Table format mechanics are central; use ../tables-io/SKILL.md.
• Model fitting or time-series analysis is central; use ../modeling-stats-timeseries/SKILL.md.

First Actions

1. Identify whether the user wants a built-in realization, current default, or custom class.
2. Keep redshift inputs scalar/vectorized and unitless unless an API expects a Quantity.
3. Preserve output quantities with units; do not strip .value until necessary.
4. For custom cosmologies, state all required parameters and units.
5. For inverse calculations, bound z_at_value and validate the solution.
6. For serialization, choose the target format and verify round-trip metadata.

References

• references/api-reference.md lists classes, functions, realizations, and I/O APIs.
• references/workflows.md covers common calculations, custom cosmologies, redshift inversion, and serialization.
• references/troubleshooting.md covers unit issues, solver bounds, default cosmology surprises, optional dependencies, and metadata round-trips.

Safety and Validation

• Always state which cosmology was used.
• Validate units on every output.
• Use bounded redshift grids/solvers for automated tasks.
• Do not assume built-in realization names are unchanged across major versions; check availability in the installed package.

Native-Backed Validation Ideas

• Evaluate Planck18.age(0) and assert it is a positive Gyr quantity.
• Compute Planck18.comoving_distance(1) and assert Mpc-equivalent units.
• Clone a realization with a new name and verify parameters/metadata.