code: function squaredDifference(left, right) {
                return left.reduce((result, val, index, arr) => { 
                  result.push(Math.pow((right[index]-val), 2));
                  return result;
                }, []);
              }
docs: (a, av) => Math.sqrt(avg(a.map(x => (x - av) * x))); 
  Returns an array of the squared different of two arrays
  @memberOf util
  @param {Number[]} left
  @param {Number[]} right
  @returns {Number[]} Squared difference of left minus right array