(https://dl.acm.org/doi/epdf/10.1145/192844.192905 although they don't call it cosine similarity; they do compute a "correlation coefficient" between two people by adding together the products of scores each gave to a post)
That being said, weirdly, the normalization by standard deviation happens outside the call to `cov` in the paper (page 181, column 1, equations (unnumbered) 1 and 2). And in equation 2 they've expanded `cov` to be the sum of pointwise multiplication of the (scores - average score) people have given to posts.
Again, not my area of expertise, just looking at the math here.
I've heard the term "cosine similarity" before but not really looked into it. What does this computation have to do with trigonometry?
(Strictly speaking we have that the angle is actually defined in terms of the dot/inner product in more abstract spaces like function spaces or L^p/l^p)