code: public static double[] minus(final double[] v1, final double[] v2) {
      assert v1.length == v2.length : ERR_VEC_DIMENSIONS;
      final double[] sub = new double[v1.length];
      for(int i = 0; i < v1.length; i++) {
        sub[i] = v1[i] - v2[i];
      }
      return sub;
    }
docs: Computes component-wise v1 - v2.
  
  @param v1 first vector
  @param v2 the vector to be subtracted from this vector
  @return v1 - v2