astropy/astropy — pull request #1369 by nden (2013-08-23 21:07:11+00:00)
Title: Sip inverse

`SIPModel` is split into two separate classes - for the forward and inverse transform.
Also this corrects the names of the coefficients; the previous version was missing an '_'.

There's also a small correction in the rotation classes so that they work now with scalars and arrays.

A bug in the inverse functions of `ShiftModel` and `ScaleModel` was fixed.