A multiple-objective linear programming model for the citrus rootstock selection problem in Florida

Citrus is one of Florida's key agricultural crops, with annual production accounting for over 70% of all U.S. production. During the 1970s and 1980s, citrus blight, tristeza and freezes caused citrus rootstock selection to become a critical issue in Florida, and it remains so today. This paper describes a multiple-objective linear programming model that we have developed for solving the citrus roostock selection problem in Florida. The model has four objective functions. These functions, together with the constraints of the model, capture the main factors that Florida citrus growers use in choosing portfolios of rootstocks for planting in their groves. We tested the usefulness of this model by solving an experimental application for the Fort Pierce area with the interactive STEM algorithm. From our research we conclude that, when properly solved with the aid of STEM, the multiple-objective linear programming model has the potential to serve Florida citrus growers as a useful decision aid in formulating rootstock selection plans. © 1997 John Wiley & Sons, Ltd.     

WHY I BELIEVE IN AN EXTERNAL WORLD

Abstract: I claim in this article that if my experience is such that it seems to me that there is an external object before me, then I have reason to believe that there is an external object before me. The sceptic argues that since my having the experience is compatible both with there being and with there not being an external object before me, I have no reason to believe that the former possibility obtains and not the latter. I respond that the sceptic has ignored a relevant difference between the two possibilities: I can make sense of the former possibility but not of the latter. I examine two broad categories of sceptical possibilities (dreams and hallucinations), explain why I cannot make sense of them, and explain why my inability to make sense of them gives me reason to believe they do not obtain.