code: public Quaterniond add(double x, double y, double z, double w) {
          return new Quaterniond(this.x + x, this.y + y, this.z + z, this.w + w);
      }
docs: Adds the double components of another quaternion to this one.
  
  @param x The x (imaginary) component of the quaternion to add
  @param y The y (imaginary) component of the quaternion to add
  @param z The z (imaginary) component of the quaternion to add
  @param w The w (real) component of the quaternion to add
  @return A new quaternion, which is the sum of both