Zhaojie Zhou,  Jiabin Song &  Yanping Chen. (2020). Finite Element Approximation of Space Fractional Optimal Control Problem with Integral State Constraint.
            <i>Numerical Mathematics: Theory, Methods and Applications</i>. <i>13</i> (4).
            1027-1049.
         doi:10.4208/nmtma.OA-2019-0201