Incremental Mean

Really cool idea, we can actually compute the mean incrementally.

The mean ${\mu }_1$, ${\mu }_2$, … of a sequence $x_1$, $x_2$, … can be computed incrementally, ${\mu }_k=\frac{1}{k}{\sum }_{j=1}^k{x}_j$ ${\mu }_k={\mu }_{k-1}+\frac{1}{k}(x_k-{\mu }_{k-1})$