Output range to compute mean, stdev, variance online. Getter methods for stdev, var cost a few floating point ops. Getter for mean costs a single branch to check for N == 0. Relatively expensive floating point ops, if you only need mean, try Mean. This struct uses O(1) space and does *NOT* store the individual elements.
Note: This struct can implicitly convert to a Mean struct.
References: Computing Higher-Order Moments Online. http://people.xiph.org/~tterribe/notes/homs.html
Combine two MeanSD's.
Mean squared error. In other words, a biased estimate of variance.
Converts this struct to a Mean struct. Also called when an implicit conversion via alias this takes place.
Simply returns this. Useful in generic programming contexts.