Estimates the unbiased population covariance from the provided two sample enumerable sequences, in a single pass without memoization. On a dataset of size N will use an N-1 normalizer (Bessel's correction). Returns NaN if data has less than two entries or if any entry is NaN.

public static double Covariance(
	IEnumerable<double> samples1,
	IEnumerable<double> samples2
)