Power

The power analysis notebook. Expanded notebook text is on [google docs](https://docs.google.com/document/d/1CQPlAue1mVFOd811cKGuy4fibFs5abR-wTjaeW6Wu0I/edit?usp=sharing).
If `dist_ids` is a numpy array, you might just be able to do fancy indexing index directly using `order[o1]`