Cosine function not implemented?

[pt]

I don't understand how cosine works. It looks like it does not implement the correct functions.

  input_matrix :thing_other,
#    :native => true,
    :similarity_func => :cosine

recommender.thing_other.process!
Traceback (most recent call last):
        1: from (irb):13
RuntimeError (implemented in subclass)

Looking at the code, it looks like there are unimplemented methods on the class. Is this expected?