diff

Computes the difference, (di = xi+k - xi) for i = 0 until x.size - k This is the discrete difference operator. For example, if k = 1, then d0 = x1 - x0, d1 = x2 - x1, ..., dx.size - 2 = xx.size -1 - xx.size -2 and returns the new array of differences.