Zhiping Qiu & Nan Jiang. (1970). A Symplectic Conservative Perturbation Series Expansion Method for Linear Hamiltonian Systems with Perturbations and Its Applications.
            <i>Advances in Applied Mathematics and Mechanics</i>. <i>13</i> (6).
            1535-1557.
         doi:10.4208/aamm.OA-2020-0282