Numerics

Matrices (and well-defined rotations) for the win.
The issue (#256) seems to be gone, see below.
![screenshot28](https://cloud.githubusercontent.com/assets/2284290/4968594/69e11cc8-6845-11e4-995b-fddd23fe9e1a.png)

We have a function Barycenter().  Please use it (several places).