Easier to talk about when class and member have different names

I have a habit of not naming internal members after the class, because it can make things harder to talk about in person -- when you say "matrix", does that mean the class Matrix or the Matrix class's internal member "matrix".

Also, it's only a Matrix once you consider the full capabilities of the class -- the array by itself is just an array, and since you are just using it for storage I would give it a dumber name like "storage_thing" or something.