Power Tools for Visualization and Decision-Making
By James J. Swain
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 behavior. 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 troubleshoot existing systems. 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 easily construct and execute models and to generate statistics and animations about results has always been one of the main attractions of simulation software.
Building a model is rarely an end in itself; instead, the goal of most analyses is to make a decision. To assist in analysis, simulation software tools are increasingly able to exchange information with other software tools in an integrated way. Simulation-modeling tools are being positioned as modeling tools within a general decision-making framework. This integration supports both analysis and the inclusion of simulation within larger contexts. For instance, simulation may be integrated with presentation software to document and report on findings or to facilitate analyses on spreadsheet or statistical software. Likewise, simulation models may be driven by solutions obtained from scheduling or optimization software and then run to provide insight into the proposed solution or to aid in the evaluation among alternative solutions. Integration speeds the process of design and design evaluation, making simulation a valuable component within the process.
Many simulation products now also include tools for data analysis for both input and output. For instance, products include distribution fitting software or convenient access to tools such as Expertfit, Bestfit or Stat::fit distribution fitting software (included in the survey). Support for run control and statistical analysis of results is also becoming more common. In the former case are mechanisms for allowing both replication of simulation runs and more complicated experimental designs. In the latter case there is support for the storage of production runs together with the ability to produce summary graphics and analysis.
Simulation is only one modeling methodology. Since simulation models operate by the construction of an explicit trajectory or realization of a process, each replication provides only a single sample of the possible behavior of a system. The accuracy of inference can be improved through repetition, so that the analysis provides a statistical estimate of any particular system parameter. This is in contrast to many analytical models that provide exact results over all possible results. This limitation is often far outweighed by the flexibility of simulation and the direct representation of entities within the simulation. In addition, because simulation directly represents a realization of the system behavior dynamically, simulation can be joined to animated outputs and used for validation, analysis and training.
The interplay between simulation and visualization is a powerful combination. Visualization adds impact to simulation output and often enhances the credibility of the model and not just for a non-technical audience. Almost all simulation software has some level of animation, from the basic to products that make you feel that you are there. Developers are already taking the next step, combining simulation to virtual reality to provide a simulation-based background for exploration, much as might be done in a training simulator.
Movies are just another type of visualization. Even here, it turns out that simulation can be a very important tool. While there is an immediate difference in the visualizations based on simulations and those used for entertainment in the former case the visual image is secondary to the constraints of the model, whereas in entertainment it is the reverse. Yet, as noted by Richard Kidd of Sony Pictures Imageworks, even here simulation methodology is immensely powerful, since even crude models can make computer-generated "special effects" more efficient and less dependent upon frame-by-frame detailing. As Kidd explains, a parameterized model provides the ability to tune the results through adjustment of parameters, potentially revolutionizing the process of generating the desired image.
As the preceding illustration suggests, the penetration of simulation is astonishing. Besides computer games and visual effects, examples of simulation appear even in the popular literature, such as the Monte Carlo simulation illustrated in the Clancy thriller "The Hunt for Red October." Or consider a recent advertisement for Budweiser, which presumes that the viewer is familiar with the notion of training simulators to make their wagon driver simulation an understandable punch line. We are led to believe that the driver is about to chase an attractive rider with his team of Clydesdales, until the "alarm" sounds and the entire scene is revealed to be only a simulation.
In the corporate world, simulation is increasingly commonplace. As Intel's Karl Kempf has observed, Intel uses simulation at all stages of product and process development, throughout the entire lifecycle of their production facilities. For Intel, simulation parallels developments in the physical process. Put simply, as the size and complexity of systems increase, simulation is no longer a luxury but a necessity for proper analysis to support good decisions. Recognizing this, the vision for simulation in the Department of Defense is even more ambitious. The DOD vision anticipates that simulation will be used for all aspects of the acquisition cycle to use simulation to evaluate designs, including the operational aspects, the manufacturing, maintenance and even tactical doctrine and training.
This survey is the fifth biennial survey of simulation software for discrete event systems simulation and related products [Swain, 1999]. Following the pattern of previous surveys, the information in the attached charts has been provided by the vendors. The survey summarizes important product features of the software, including price. 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 47 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 give a general gauge of the product's capability, special features and usage. This year we have added questions about experimental run control (e.g., batch run or experimental design capabilities) and special viewing features, including the ability to produce animations or demonstrations 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/orms/surveys/Simulation/Simulation.html) and includes vendors who missed the publishing deadline. Of course, most of the vendors provide their own Web sites with further details about their products.
This survey is not a review of the products or a comparison of their relative merits. Such a project would be a large undertaking, one that would have to take into account the general qualities of the software as well as the fitness of specific products for particular classes of problems. Discussions with a number of consulting firms suggest that they themselves have more than one tool available, depending upon the client requirements and the special features of the problem. An attempt has been made to provide some side-by-side comparisons of software for several distinct problems. These comparisons have been published by Simulation News Europe and are also available on the Web site www.argesim.org/comparisons.
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 application. 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.
In addition to users groups, there are a number of organizations and conferences devoted to the application and methodology of simulation. The INFORMS publications Management Science, Operations Research and Interfaces publish articles on simulation. The INFORMS College on Simulation sponsors sessions on simulation at the national meeting and makes awards for both the best simulation publication and service awards in the area, including the Lifetime Achievement Award for service to the area of simulation. Further information about the College on Simulation can be obtained from the Web site www.informs-cs.org. This site now provides the complete contents of the proceedings of the conference for the last three years and also contains links to many vendors of simulation products and sources of information about simulation, simulation education and references about simulation.
The College is also a cosponsor of the annual Winter Simulation Conference. The conference will be held Dec. 9-12 at the Crystal Gateway Marriott in Arlington, Va. The program includes tutorial, methodology and applications tracks. Further information and registration information is available from the site www.wintersim.org. The sponsors of the conference are also ready sources of information about simulation and they can be linked from the Winter Simulation Conference Web site.
Changing corporate scene
In addition to the changes in products in the survey, the corporate world of simulation has undergone significant changes in the last few years, as many of the well-known names of simulation have been acquired by larger concerns. For instance, Pritsker Corporation has been a division of Symix (itself newly renamed Frontstep) for several years, while Systems Modeling is now a division of Rockwell Software, and Autosimulations is now a part of Brooks Automation. These acquisitions often provide a stronger financial base for the divisions to promote and develop their products. Meanwhile, CACI has reorganized its software sales, selling several of its products and is emphasizing its large governmental consulting services.
The simulation software market appears to be fairly well established and international. Within this market, it appears that simulation software is now a standard software category, much as a spreadsheet program or a word processor is in the general business software environment. As with spreadsheets and word processing software, simulation software needs to work well with the other programs within the suite of software used in analysis. Beyond working with business software, changes to several of the products suggests that simulation tools will be increasingly linked to other decision software, such as production scheduling software.
James J. Swain is professor and chair of the ISEEM department at the University of Alabama in Huntsville. He is active in the INFORMS College on Simulation and is a member of the Board of the Winter Simulation Conference. E-mail: firstname.lastname@example.org.
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