Control Theory, Second Edition

The literature on optimisation is very extensive. The bibliography lists two books that are concerned with inequalities, since a study of these is a prerequisite for understanding certain approaches to optimisation. The references are Beckenbach and Bellman (1961) and Hardy, Littlewood and Polya (1967).
There are useful early books on specific topics in optimisation; for instance, Hestenes (1966) on the calculus of variations, Pontryagin et al. (1964) on the maximum principle and Bellman (1957) on dynamic programming.
Recommended general texts are Bryson (2002), Markus and Lee (1967) and Sage and White (1977). Grimble and Johnson (1988) is a very comprehensive two-volume set.
Finally, I mention Pallu de la Barri re (1967), still in print. This book, by making mathematical demands on the reader, may act as a motivator for those who need a concrete reason for studying further mathematics.