Comments on "A discrete optimal control problem for descriptor systems" [with reply]

In the above-mentioned work (see ibid., vol.34, p.177-81 (1989)), necessary and sufficient optimality conditions are derived for a discrete-time optimal problem, as well as other specific cases of implicit and explicit dynamic systems. The commenter corrects a mistake and demonstrates that there is not an 'if and only if' correspondence between stationarity conditions and minimization of the Hamiltonian. In replying, Lin and Yang acknowledge this and also give a version of theorem two in the context of their response to achieve a balance.<
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