Documentation: write up methods for single subject region model

[andy-sweet]

Before writing up specs, designs, tests or implementations, we need to start by writing up a methods section that describes our mathematical models.

First, I'll write up the model for anomalous regions that differ across the patient pool. This is the work of my thesis and our MICCAI 2013 paper. I'll use notation from the MICCAI paper as this is more consistent with the notation in the previous papers.

While this will initially be specific to this model, I will write it with the intention that we want to write up the other models too.

[andy-sweet]

Closing this for now, but further changes may occur after proof reading the docs.