code: public static double[] minusEquals(final double[] v1, final double s1) {
      for(int i = 0; i < v1.length; i++) {
        v1[i] -= s1;
      }
      return v1;
    }
docs: Subtract component-wise in-place v1 = v1 - s1,
  overwriting the vector v1.
  
  @param v1 original vector
  @param s1 Value to subtract
  @return v1 = v1 - s1