A Three-Phase Simulation System Written
John G. Crookes, David W. Balmer, Sew Tee Chew, Ray J. Paul · 1986
A three-phase simulation system written in Pascal for use on microcomputers, minis and mainframes is presented. The advantages of the three-phase method are discussed, and the basis of the system explained. Although a traditional, textbook example is used to aid explanation and discussion, the system described in this paper has been used in real applications and in the teaching of simulation at Lancaster University and the London School of Economics. It also provides a basis for further research in simulation within both institutions. The Computer Aided Simulation Modelling (CASM) project team at the London School of Economics are embarked on research into making the process of simulation modelling more efficient. A description of the aims of this project are given by Balmer and Paul,' and an outline of its relationship with artificial intelligence by Balmer.2 Doukidis and Paul3 and Paul and Doukidis4 report on early and more recent attempts at automating simulation problem formulation using expert systems and natural language understanding systems. Early decisions of the CASM team included the choice of computing environment within which initial work should proceed. Apple II microcomputers were easily available and offered in the UCSD p-system a convenient environment for rapid program development. The recent paper by Crookes and Valentine' discusses the virtues of microcomputer-based simulation modelling by using an application to illustrate the points made. Within this environment, the Lancaster system provided a sound initial basis for further exploratory work. The system is written in Pascal, with all its advantages as detailed by O'Keefe,6 among others, and the simulation model structure is the three-phase method, the merits of which are discussed in the next section. The CASM team have made the Lancaster system available on the Sirius, Apricot, I.B.M. P.C. and B.B.C. microcomputer (Z80 version) as well as a VAX. The system works under the UCSD, CPM, PCDOS and MSDOS operating systems on microcomputers, and VMS on the VAX. The listings in the Appendices relate to the VAX version. As the CASM team have worked with LANCASTER, modifications and additions have been made. These are described in a later section of the paper, under the heading eLSE, an extended Lancaster Simulation Environment. eLSE has been tested in practical environments such as military modelling, and in a port simulation, as described by Paul and Balmer7 and El Sheikh et al.8 An interactive simulation program generator (I.S.P.G.) called LANGEN has been written for eLSE, and is described by Chew et al.9 It owes much in its external form and concept to the pioneering work of Clementson10 in his I.S.P.G. called CAPS. It is currently used to support the teaching of simulation to undergraduate and postgraduate students at the School.