References
- Greenberg , H.J. and Pierskalla , W.P. 1971 . A review of quasi-convex functions . Operations Research , 19 : 1553 – 1570 .
- Mangasarian , O.L. 1969 . Nonlinear programming , New York : Mc Graw-Hill .
- Roberts , A.W. and Varberg , D.E. 1973 . Convex functions , New York : Acad. Press .
- Rockafellar , R.T. 1972 . Convex analysis , New Jersey : Princeton Univ. Press .