Cobweb Diagrams in Excel

David Gurney

Department of Mathematics
Southeastern Lousiana University
dgurney@selu.edu

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ABSTRACT

Iterative functions are often used to simulate the dynamics of human and animal populations. Unfortunately, if the iterative function is no more complicated than a two-term quadratic, trying to predict the results of repeated application of the function is very difficult. Even studying the numerical results of applying the function again and again may not provide much insight into the long-term behavior of the populations. Cobweb diagrams offer a way around this dilemma. Originally devised for use with rulers and graph paper, cobweb diagrams provide a relatively quick way of representing the repeated application of an iterative function. This talk will demonstrate how to create cobweb diagrams using a Microsoft Excel spreadsheet. The strong and weak points of this method of creating cobweb diagrams, as opposed to using the TI-83 graphing calculator or software programs like Maple and Mathematica, will also be discussed.

Keyword(s): dynamical systems, spreadsheets