Karl Kunisch, Wenbin Liu, Yanzhen Chang, Ningning Yan and Ruo Li. (2010). Adaptive Finite Element Approximation for a Class of Parameter Estimation Problems.
            <i>Journal of Computational Mathematics</i>. <i>28</i> (5).
            645-675.
         doi:10.4208/jcm.2009.10-m1016