Overlay chart from Decisioneering's Crystal Ball 7, an Excel-based simulation program (www.crystalball.com).

We are used to thinking about simulation as a powerful tool for letting us imagine new systems and allowing us to both quantify and observe their behaviors. Whether the system is a production line, a distribution network or a communications system, simulation can be used to study and compare alternative designs or to trouble shoot existing systems. Simulation is used extensively by industry and the government for experimentation, visualization, exploration and training, taking advantage of advances in animation and computer processing to make this possible. With simulation models we are free to imagine how an existing system might perform if altered or imagine and explicitly visualize how a new system might behave before the prototype is even completed. The ability to construct and execute models, and to generate statistics and animations about results, has always been one of the main attractions of simulation software.

Games such as America's Army also illustrate that simulation is increasingly being used to immerse the players (or analysts) within the simulated environment, to provide a detailed visual experience that is useful for both trouble shooting as well role playing. They are also structured to provide interaction between multiple players. Outside of entertainment, the players may be other models. For instance, military models are increasingly composed of multiple, distributed models that may represent different operational units or models for disparate items such as sensors, aircraft and ships. Infrastructure software is used to mediate the exchange of information between the models and to coordinate the time advance.

Survey

	Flexsim's simulation model of a distribution center. The model is used to determine staff, picking wave times, wave quantities, resource utilization and material handling capabilities.

This survey is the seventh biennial survey of simulation software for discrete-event systems simulation and related products (Swain, 2003). The survey summarizes important product features of the software, including price. All product information has been provided by the vendors. Products that run on desktop computers to perform discrete-event simulation have been emphasized, since these are the most suitable for usage in management science and operations research. Simulation products whose primary capability is continuous simulation (systems of differential equations observed in physical systems) or training (e.g., aircraft and vehicle simulators) are omitted here.

There are 48 products listed in the survey, making it one of the larger surveys in the series. The range and variety of these products continues to grow, reflecting the robustness of the products and the increasing sophistication of the users. The information elicited in the survey is intended to provide a general gauge of the product's capability, special features and usage. This survey includes information about experimental run control (e.g., batch run or experimental design capabilities) and special viewing features, including the ability to produce animations or demonstration that can run independent of the simulation software itself. A separate listing gives contact information for all of the vendors whose products are in the survey. This survey is also available on the Lionheart Publishing Web site (www.lionhrtpub.com) and will include vendors who missed the publishing deadline. Of course, most of the vendors provide their own Web sites with further details about their products.

Like all software, the relation between the vendor and the user is ongoing. Products evolve over time, and new versions of the software become available periodically. In addition, the vendor is a source of information about both its products and their applications. Most vendors now maintain contact with their users through mailings, newsletters, their own Web sites and annual user group conferences. These conferences showcase the application and usefulness of the products, nurture contact with the users, and provide a way for users to learn from each other.

A number of technical and professional organizations and conferences are devoted to the application and methodology of simulation. The INFORMS publications Management Science, Operations Research and Interfaces publish articles on simulation. The INFORMS Simulation Society sponsors simulation sessions at the national INFORMS meeting and makes awards for both the best simulation publication and recognition of service in the area, including the Lifetime Achievement Award for service to the area of simulation. Further information about the Simulation Society can be obtained from the Web site www.informs-cs.org. This site now provides the complete contents of the Proceedings of the Winter Simulation Conference from 1997 to 2004, the complete final program for 2005, and also contains links to many vendors of simulation products and sources of information about simulation, simulation education and references about simulation. The Society for Modeling and Simulation International (www.scs.org) is also devoted to all aspects of simulation. Their conferences include the Huntsville Simulation Conference that takes place annually in Huntsville, Ala.

The Simulation Society and the Society for Modeling and Simulation are sponsors of the annual Winter Simulation Conference, held this year in Orlando, Fla. The 2005 program included tutorial, methodology and applications tracks, and featured specialized areas such as computer modeling, financial models, transportation and logistics and other operations. The sponsors of the conference are also ready sources of information about simulation. The sponsor Web sites are linked from the Winter Simulation Conference Web site.

The Discipline of Simulation


The phenomenal growth of simulation throughout the industry and particularly within the Department of Defense (DoD) has led to a growing demand for simulation professionals to develop models and modeling tools, and to manage large and complex simulation-based projects. Lacking a source of simulation professionals, the traditional approach has been to re-train engineers, scientists or programmers in the specialized skills needed for a given modeling or software development effort. In the case of manufacturing and service fields where discrete-event simulation is the predominant approach, many of these skills could be obtained as part of a degree program in industrial engineering, operations research or management science. In these programs simulation was a component of an overall program, not the end in itself. In a similar manner, expertise in communications or radar simulation might be developed by recruiting and retraining generalists from physics or electrical engineering.

The need for simulation professionals appears to be outstripping the supply that can be provided through the traditional approach. For instance, a survey of job advertisements over a limited study period turned up more than 100 local firms looking for professionals to do simulation (Madewell and Swain, 2003) in the Huntsville, Ala., area alone. An analysis of the advertisements characterized both types of professionals sought (developer, analyst and manager) and the qualifications sought by the employers.

Simulation application far transcends the methods favored by individual disciplines, such as operations research. In fact, application areas and their disparate simulation approaches have sub-divided simulation, but there is an increasing sense that modeling and simulation may constitute a discipline in itself. Academic programs in Modeling and Simulation have appeared at the University of Arizona, University of Central Florida, Old Dominion University, Georgia Tech and the University of Alabama in Huntsville to name a few. In the last several years informal "simulation summits" of interested educational, governmental and industry representatives have been held to consider what common body of knowledge characterized simulation and steps that could be taken to recognize this field as a specialty. Certification in Modeling and Simulation is now being offered, and the DoD is considering a job designation (CP-36) that would identify the particular skills and knowledge of a modeling and simulation professional. Organizations such as the Alabama Modeling and Simulation Council (www.amsc.to) are cover-all aspects of simulation, including the industry, technical standards and training, academics and training and applications.

Remember the Titans!


The simulation software industry is only about a half century old. We can take Geoffry Gordan's development of the GPSS simulator, first made publicly available by IBM in 1961, as a convenient starting point. SIMSCRIPT soon joined GPSS as a commercial product, and many others have since joined them. Both have undergone many changes, but it is a tribute to the power of these two products that they still flourish in the marketplace.

Digital simulation predates the publicly available products by about a decade. We noted the passing of one of the early figures of simulation, Dr. A. Alan B. Pritsker, in the last survey. An appreciation of his career (Wilson and Goldsman, 2001) was included as a part of a special issue of the IIE Transactions honoring him. Other important figures have been honored over the years through the INFORMS Simulation Society Lifetime Achievement Awards. In the last few years, the Winter Simulation Conference has organized sessions devoted to the developers of simulation from the early years or having made significant contributions to simulation practice over the years. These sessions have now been renamed the Titans of Simulation session. Last year's speakers included Phil Kiviat and Dev Pillai; this year's Titans are Denis Pegden and Jack P. C. Kleijnen.

• Simulation Software Survey

James J. Swain (jswain@ise.uah.edu) is professor and chair of the ISEEM department at the University of Alabama in Huntsville.

References

1. Madewell, Charles D., and J. J. Swain, 2003, "The Huntsville Simulation Snapshot: A Quantitative Analysis of What Employers Want in a Systems Simulation Professional," Modeling and Simulation, Vol. 2, No. 2, April-June 2003.
   
   
2. J. J. Swain, 2003, "Simulation Reloaded: Sixth Biennial Survey of Discrete-Event Simulation Software," ORMS Today, Vol. 30, No. 4, August 2003, pgs. 46-49.
   
   
3. Wilson, J. R. and Goldsman, D. (2001), "Alan Pritsker's Multifaceted Career: Theory, Practice, Education, Entrepreneurship, and Service," IIE Transactions, Vol. 33, No. 3, pgs. 139-147.

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