1. A. P. Sage and C. C. White III:Optimum Systems Control, 2nd ed., Prentice-Hall, Englewood Cliffs, NJ, 1977, pp. 48–50.
2. A. P. Sage and C. C. White III:Optimum Systems Control, 2nd ed., Prentice-Hall, Englewood Cliffs, NJ, 1977, pp. 58–60.
3. A. P. Sage and C. C. White III:Optimum Systems Control, 2nd ed., Prentice-Hall, Englewood Cliffs, NJ, 1977, pp. 103–06.