Returns the sample covariance of a data set. The size of the input array should be 2. The function eliminates all pairs for which either the first element or the second element is empty. After the elimination, if the length of the input is less than 2, the function returns the empty sequence.
For the version of this that uses range indexes, see cts.covariance.
var arr = new Array();
for (i=1; i < 11; i++) {
var x = new Array();
var j = 2 * i;
x.push(i, j);
arr.push(x); };
math.covariance(arr);
=> 18.3333333333333