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2. V. I. Agoshkov, Methods of Optimal Control and Adjoint Equations in Problems of Mathematical Physics (IVM RAN, Moscow, 2003) [in Russian].
3. J.-L. Lions, Quelques methods de Resolution des Problemes aux Limites Nonlineares (Dunod, Paris, 1968).
4. G. I. Marchuk, Adjoint Equations and Analysis of Complex (Kluwer, Dordrecht, 1995).
5. A. F. Bennett, Inverse Modeling of the Ocean and Atmosphere (Cambridge University Press, Cambridge, 2002).