Is there something wrong in your code? I don't see the effect.

smile> val x = Array(1.0, 2.0, 3.0, 4.0)

x: Array[Double] = Array(1.0, 2.0, 3.0, 4.0)

smile> val y = Array(4.0, 3.0, 2.0, 1.0)

y: Array[Double] = Array(4.0, 3.0, 2.0, 1.0)

smile> x + y

res2: smile.math.VectorAddVector = Array(5.0, 5.0, 5.0, 5.0)