code: def _q_to_dcm(self, q):
          
          assert(len(q) == 4)
          arr = super(Quaternion, self)._q_to_dcm(q)
          return self._dcm_array_to_matrix3(arr)
docs: Create DCM (Matrix3) from q
          :param q: array q which represents a quaternion [w, x, y, z]
          :returns: Matrix3