A Case of Interaction between Systems Dynamics and Linear Programming: The Rapim-Pirenaica Model1

This objective of this paper is to reproduce the functioning of a farm which mixes agriculture with livestock-raising. Furthermore, it attempts to integrate, within the framework of a dynamic simulation model, the resolution of a problem of linear programming that yields the optimum mix of crops and livestock that satisfies the given set of restrictions. The aim of this exercise is to maximize the total value of the output of a farm that produces 16 different economic goods. This exercise considers 10 constraints including, among others, the following: the initial herd size for each type of animal; the amount of land devoted respectively to cultivation, forest, and pasture; the average returns of each crop; the restrictions on crop rotation; and the available amount of familial and extra-familial labor. The physical returns of the crops, the sale price of each crop and each type of animal, and wages, are exogenous data. Since this model is written in the program Vensim, the above-mentioned optimization model will be dealt with utilizing Vensim’s external functions, calling for a function C of lineal programming problems