APPENDIX 1. Software

NOTE ON THE MP-MAS SOFTWARE

MP-MAS was encoded in C++ by Thomas Berger with contributions from Pepijn Schreinemachers and Thorsten Arnold. It is freeware that can be downloaded from http://www.uni-hohenheim.de/mas/software. A manual is available electronically from the same location. The software is a single executable file that does not need installation. Both a Windows and a Unix version are available and the program runs on any personal computer. For very large models, the use of Unix OS is recommended as the software runs more stable.

MP-MAS uses mathematical programming software, which needs to be preinstalled. Currently, the Optimization Solutions Library (OSL) is used, which gives a high performance on very large models and can handle many integers (Wilson and Rudin 1992). IBM, the producer of OSL, has stopped the development of this software and transferred parts of the code to an open source community (http://www.coin-or.org/resources.html). This new solver platform, called COIN, is currently being implemented in MP-MAS to replace IBM-OSL.

The number of agents in the downloadable version is limited to 50. MP-MAS is not yet open source but interested academic software developers can join the group’s effort and contribute to the software’s development. People interested in applying the software to their own research area are also encouraged to get into touch and potential extensions of the software to a particular application can be discussed.

The software is constantly being improved: additional features are added with each new application, the input files contain more explanatory information, the error handling of the program is improved, and more powerful solvers (all freeware) are being integrated. Although the model has integrated many new features in recent years, empirical applications will often require additional ones.

USE OF THE MANUAL

The purpose of the manual is to make MP-MAS more widely accessible and increase its use by other researchers. The MP-MAS does not have an own graphical user interface (GUI). Instead, Microsoft Excel workbooks are used to organize the data and to setup simulation experiments while the MP-MAS can be run using simple command line functions.

The advantage of using Microsoft Excel workbooks is that most users are familiar with it, that it is relatively easy to make changes, and that explanatory notes are easily inserted into the files. Workbooks are easily linked and can contain separate sheets for calculations and documentation of the model. The disadvantage is that `small changes can have big consequences’; that is, accidentally entering a value in the wrong place can make the program crash.

To avoid this, the user is advised to start with a basic set of default input files that contain most of the features of the model and then to stepwise adjust this to the own application while trying to run the model at each step. For instance, the MP model can be gradually expanded to include more livestock and crop enterprises. Running the model after each significant change helps to locate possible errors more easily as the program’s error calls can sometimes be cryptic and it is therefore difficult to pinpoint an error after making many changes at a time.