vec1

Array
(
    [0] => 2
    [1] => 4
    [2] => 6
    [3] => 8
)

vec2

Array
(
    [0] => 3
    [1] => 9
    [2] => 27
    [3] => 81
)

mass(vec) - expected 20, actual 20
mean(vec) - expected 5, actual 5
variance(vec) - expected 6.666, actual 6.6666666666667
stdev(vec) - expected 2.581989, actual 2.5819888974716
covariance(vec1, vec2) - expected 84, actual 84
correlation(vec1, vec2) - expected 0.9165151, actual 0.91651513899117