On: Gaussian distributions are monoids and why machine learning experts should care

[afc]

Would somebody explain this step in his explanation?

http://izbicki.me/blog/wp-content/plugins/optimized-latex/im...

How does he go from (a - b)^2 to a^2 - b^2? What am I missing?

[jgeralnik → afc]

That's the definition of variance. Look here: http://en.wikipedia.org/wiki/Variance#Definition

[andrewcooke → afc]

b in the case given is the mean. so it's defined as sum(a)/n. so the "ignored" term is sum(a-sum(a)/n)) which is zero.