cosmo - GoDoc

Overview ¶

Package cosmo implements basic cosmology calculations in Go.

FLRW is the basic interface type that defines the key cosmological functions common to all supported cosmologies.

The Friedmann-Lemaître-Robertson-Walker (FLRW) metric is the general form that all homogenous, isotropic, connected cosmologies follow.

https://en.wikipedia.org/wiki/Friedmann-Lema%C3%AEtre-Robertson-Walker_metric

Provides:

FlatLCDM  (H0, OM); OL = 1-OM, OK=0
LambdaCDM (H0, OM, OL, OK); w = -1
WCDM      (H0, OM, OL, W); w = w0
WACDM     (H0, OM, OL, W0, WA); w = w0 + w_a * (1-a)

Equations and numerical formulae based on

Hogg, https://arxiv.org/abs/astro-ph/9905116
Feige, 1992, Astron. Nachr., 313, 139.
Eisenstein, 1997, https://arXiv.org/abs/astro-ph/9709054v2
Mészáros & Řípai 2013, A&A, 556, A13.
Baes, Camps, Van De Putte, 2017, MNRAS, 468, 927.
Kantowski, 2000, https://arxiv.org/abs/astro-ph/0002334
Thomas and Kantowski, 2000, PRD, 62, 103507.  Eq. 3

Organizational thoughts based on code in astropy.cosmology

http://docs.astropy.org/en/stable/_modules/astropy/cosmology

Performance Notes:

1. Calculating a single line-of-sight comoving distance takes from 890ns - 260µs, depending on the complexity of the cosmology. Analytic cases take ~1µs, while explicit integration is ~200µs.

FlatLCDM      892ns  (analytic for OM<1)
LambdaCDM     139µs
WCDM          250µs
WACDM         261µs

These numbers are based on the output of `go test -bench ComovingDistance` run on a 2015 MacBook Air: dual-core 2.2 GHz Intel Core i7, 8 GB 1600 MHz DDR3; with Mac OS X 10.13.2 and go 1.9.2

2. The current types FlatLCDM, LambdaCDM, WCDM, WACDM implement their methods as value receivers. There's a mild performance hit for using value receivers instead of pointer receivers. This performance penalty is 40% for individual calls to E or Einv but this penalty is only 1-2% for calls to the general *Distance methods.

For now the use case model seems more amenable to value receivers -- conceptually, the cosmologies should be immutable -- and the performance penalty is acceptable.