on the angular distance

[Gerry Yu]

In the newest edition, the angular distance is calculated
with a simplizied formular, which only allow \omega_k_0 > 0.
(equation 19 of David Hogg's arXiv:astro-ph/9905116v4)
This limits the application of angular distance and the
 luminosity distance on cosmological constrains.
A more general approach is deriving the angular distance
from equation 18 directly. And the transversed comoving
distance need a slight revisement also.

the corresponding function should be

def comoving_distance_transverse(z, z0=0, **cosmo):
     d_c = comoving_distance(z, z0, **cosmo)
     .....

def angular_diameter_distance(z, z0 = 0, **cosmo):
    dm  = comoving_distance_transverse(z, z0, **cosmo)
    return dm / (1. + z)

[Roban Kramer]

Sorry for the long delay in responding. I've made the appropriate change to angular_diameter_distance (while preserving the code for the angular diameter distance between two objects at z>0 for omega_k_0 > 0). A quick test looked okay. Let me know if you have any trouble with it. New version is 0.1.104.

-Roban

To see the changes, go to:

https://github.com/roban/CosmoloPy/commit/781968a5589fb2de374243159c6caba081e707f1#diff-0

--
Roban Hultman Kramer | Zwicky Fellow | Institute for Astronomy
ETH Zürich (Swiss Federal Institute of Technology)