EXAMPLE Happel and Jordan (1975) reported an objective function (cost) for the design of a dis- tillation column as follows: f = 14720(100 P) + 6560R - 30.2PR + 6560 30.2P + 19.5n (5000R - 23PR + 5000 23P)0.5 + 23.2 ( 5000R 23PR + 5000 23P]0.62 ( - where n = number of theoretical stages R = reflux ratio P = percent recovery in bottoms stream They reported the optimum occurs at R = 8, n = 55, and P = 99. Is f convex at this point? Are there nearby regions where f is not convex