General, commonly used functions for other projects.

## Project description

Quickly calculate cosmological parameters.

• Provides both command-line and API interfaces.
• Uses the machinery from the astropy.cosmology package.

The user provides an input parameter (e.g. redshift or luminosity-distance) and recieves the entire set of cosmological measures corresponding to the epoch thus specified.

The below gif shows three examples: inputting a redshift, a luminosity distance (-dl 400Mpc), and an age of the universe (-ta 3.2Gyr).

## Installation

Using pip:

```pip install cosmopy
```

From source:

```git clone git@github.com:lzkelley/cosmopy.git
pip install cosmopy
```

## Usage

cosmopy can be used via the command-line cosmo command, or via python API by importing the module directly.

• Command Line:

```\$ cosmo --help

usage: cosmo [-h] [-z Z] [-a A] [-dc DC] [-dl DL] [-tl TL] [-ta TA] [-v]

cosmopy: cosmological calculator.

optional arguments:
-h, --help      show this help message and exit
-z Z            target redshift z
-a A            target scale factor a
-dc DC, -cd DC  target coming distance D_C
-dl DL, -ld DL  target luminosity distance D_L
-tl TL, -lt TL  target look-back time T_L
-ta TA, -at TA  target universe age T_A
-v, --version   print version information.
```

For example, entering an input redshift of 0.2:

```\$ cosmo -z 0.2

z = 0.2000                                : Redshift
a = 0.8333                                : Scale-factor
D_c = 815.3960 Mpc      ~ 2.5160e+27 cm     : Comoving Distance
D_L = 978.4752 Mpc      ~ 3.0193e+27 cm     : Luminosity Distance
D_A = 679.4967 Mpc      ~ 2.0967e+27 cm     : Angular Diameter Distance
Arcsec = 3294.2928 pc      ~ 1.0165e+22 cm     : Arcsecond Scale
T_lb = 2.4277 Gyr        ~ 7.6613e+16 s      : Lookback Time
T_a = 11.3235 Gyr       ~ 3.5734e+17 s      : Age of the Universe
DM = 39.9527                               : Distance Modulus
```

or an input luminosity-distance of 400 Mpc:

```\$ cosmo -dl 400Mpc

z = 0.0880                                : Redshift
a = 0.9192                                : Scale-factor
D_c = 367.6631 Mpc      ~ 1.1345e+27 cm     : Comoving Distance
D_L = 400.0000 Mpc      ~ 1.2343e+27 cm     : Luminosity Distance
D_A = 337.9403 Mpc      ~ 1.0428e+27 cm     : Angular Diameter Distance
Arcsec = 1638.3809 pc      ~ 5.0555e+21 cm     : Arcsecond Scale
T_lb = 1.1496 Gyr        ~ 3.6280e+16 s      : Lookback Time
T_a = 12.6016 Gyr       ~ 3.9768e+17 s      : Age of the Universe
DM = 38.0103                               : Distance Modulus
```
• Python API

The module can be imported as cosmopy, from which the primary access point is the api function which accepts two arguments: a key (a target cosmological parameter) and a value of that parameter (optionally including units). The function returns a dictionary with the computed values as key: value pairs (both strings). For example:

```\$ python -c "import cosmopy; print(cosmopy.api('dl', '1.2 Gpc'))"
{'z': '0.2396', 'dl': '1200.0000 Mpc', 'tl': '2.8359 Gyr', 'dc': '968.0336 Mpc', 'ta': '10.9153 Gyr', 'da': '780.9075 Mpc', 'dm': '40.3959', 'arc': '3785.9464 pc', 'a': '0.8067'}
```