code: public static Complexd fromRotationTo(Vector2d from, Vector2d to) {
          return fromAngleRad(TrigMath.acos(from.dot(to) / (from.length() * to.length())));
      }
docs: Creates a new complex from the angle defined from the first to the second vector.
  
  @param from The first vector
  @param to The second vector
  @return The complex defined by the angle between the vectors