r = cov(X，Y) / √[D(X)D(Y)]

Covariance of molecules x and y

The denominator is the standard deviation of x times the standard deviation of y.

Correlation coefficient r∈[- 1, 1]

If x and y are independent of each other, then r=0.

If r=0, then x and y are linearly independent, but not necessarily independent of each other.