Xiaomin Duan, Huafei Sun & Zhenning Zhang. (1970). A Natural Gradient Descent Algorithm for the Solution of Lyapunov Equations Based on the Geodesic Distance.
            <i>Journal of Computational Mathematics</i>. <i>32</i> (1).
            93-106.
         doi:10.4208/jcm.1310-m4225