1. “The Mathematical Theory of Optimal Processes.”;Pontryagin,1962
2. R. E. Kalman, The theory of optimal control and the calculus of variations. R.I.A.S. Tech. Rept. No. 61-3 (1961).
3. “Calculus of Variations.”;Gelfand,1963
4. For further references, see IEEE, Trans. Auto. Control9 (1964); J. Basic Eng. (1964).