The growing popularity of using simulation as a modeling and problem analysis tool has resulted in a vast and growing availability of simulation software on the market. As these software usually represent considerable expenses for companies that acquire a license to use them, their proper selection becomes one of the key factors in the success of simulation projects (and the employment of the responsible team!) to be developed in the future. Therefore, this selection should be made more and more based on objective criteria, taking into account not only the characteristics of the products but also the applications that are intended to be developed. As in any complex decision situation, information is a key factor, which is the main objective of this work: to provide basic information about these products and, more importantly, to contribute to a more efficient information search process.
Our main interest is discrete event simulation software. However, depending on the application, one should not disregard the possibility of using electronic spreadsheets (EXCEL® and others) and accessory products (such as @RISK from Palisade Corporation), especially in the case of simpler situations in which the time variable does not is relevant (so-called “one-shot simulations”) or situations where the clock can be changed at constant intervals. In addition, mention should also be made of statistical support software for simulation, such as those used to identify probability distributions for input data (eg BestFit and ExpertFit) or aimed at better analysis of results and experimentation.
Today, with a micro Pentium, in a standard configuration (32Mb of RAM), we already have a machine capable of processing quite complex and previously unimaginable applications. However, software has come to represent a crucial factor in the use of simulation. Thus, although there are currently good products on the market, their greater sophistication, combined with an increasingly high cost, has made the choice of simulation software a difficult decision. Previously, the difficulty that resided in a reduced number of options: General Programming Languages (FORTRAN, Pascal,...), or a few Specific Languages for Simulation (GPSS, SIMULA, GASP, SLAM) has today been transferred to a difficult and sometimes expensive choice among a large number of products and a permanent effort to update these products.
GENERAL SIMULATION SOFTWARE
We can divide the simulation software available today into two broad categories:
• Of a general nature (focused here);
• Focused on specific applications, such as manufacturing, services, telecommunications, re-engineering and others.
General software is, of course, the best known. With the certainty that we are (not intentionally!) omitting several of these products, we present in the table below a list (in alphabetical order) of the main software, responsible company, Homepage address (when available) and the information we have regarding the existence of representative in Brazil. Most of the companies mentioned are specialized in simulation, also offering other products – such as simulators aimed at specific applications, derived from general software – and services – such as consultancy and training. Almost all of these software have demos available, either through direct contact with the company, its representative, via the internet (beware that, in general, they are heavy files!). In any case, a practical and quick way to find out more about each of these products is by visiting the respective Homepages and related “sites”.
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GENERAL CHARACTERISTICS OF THE PRODUCTS
Some striking features are common to most products that compete in this rich market. Among them we mention the search for a working environment that is as friendly as possible, preferably a Windows application, with facilities for modeling, debugging, visualization of the execution, statistical analysis of results and generation of reports.
But arguably the most commercially appealing feature is the animation features. These range from simple implementations with graphical symbols (circles, squares, etc.) flashing on the screen and showing numerical values that describe the state of the system (size of queues, for example), to sophisticated 3-D animation resources that, obviously, they demand high computational effort and make the product more expensive. Our attitude towards this trend is somewhat conservative: from a certain level of animation sophistication, we see few additional advantages for a simulation study, including the risk of diverting attention from the model's logic to its visualization. But we also recognize the seductive power of an animated output, in such a way that a compromise solution between the two extremes (no animation or sophisticated animation) seems to us the best alternative.
Still with regard to animation systems, while most systems (Ex: Arena, ProModel, Automod, Taylor) allow the visualization of the simulation in “real time”, that is, while it is running, another option is the use of an animator “offline” as is the case with PROOF Animation by Wolverine (the same company that produces GPSS/H, a new version of the old GPSS). In the case of PROOF, the animator program reads data from a text file (trace file), generated by a previous simulation run, and, based on this data plus a lay-out file, enables an animated visualization of the simulation. This option applies to GPSS, but can also be used with other software, such as SIMUL (Saliby, 1996); for this, the simulation just generates the text file (trace file) in the format required by PROOF.
Another striking feature of these new products, and in that they are more similar to each other, concerns the modeling/programming stage. In this case, there is generally a vast library of modeling/programming blocks that are selected via the menu, positioned and connected via the mouse (“drag and drop”). It is also up to the user to fill in the necessary additional data, in windows associated with each of these blocks. But, don't get excited! In a real application, the user will always have some programming to do, contrary to what software vendors usually claim! And then, practical difficulties may arise, as the user may be forced to decipher a simulation code generated in the specific language of the application and know how to make the necessary changes. In general, this intervention requires a degree of software knowledge that goes far beyond knowledge of the basic modeling/programming blocks.
SOME SUGGESTIONS
Jerry Banks (1997), one of the authors who have written most on the subject, provided a list of factors to be considered when selecting a simulation software, each of which is described by a set of characteristics. A summary of these factors follows:
• Input:
Mouse point and click feature;
Use of CAD drawings;
File import;
File export;
Understandable syntax;
Interactive execution control;
Interface with another language;
Feature for input data analysis.
• Processing:
Possibility of complex modeling (Powerful constructs);
Velocity;
Flexibility in running races;
Generation of random values;
Resetting statistics and generators (Reset);
Independent replications;
Global and attribute variables;
Programming: logical flexibility;
Portability
• Output:
Standardized reports;
Customized reports (“customized”);
Graphic generation;
Maintenance of databases;
Collection of the result of mathematical expressions;
Application-specific (“custom”) performance measures;
Output to files.
• Environment:
Ease of use;
Ease of learning;
Quality of documentation;
Animation features;
“Run Time” version.
• Software vendor:
Stability;
History;
“Track record”;
Support.
• Cost:
Acquisition of license;
Updates;
Training and support.
Other authors provide additional suggestions, highlighting the following factors:
• Use of templates for faster modeling;
• Use of object-oriented programming concept;
• Interface with other software tools (CAD, spreadsheets, …)
• Experimental optimization features;
• Internet applications;
• Real-time control.
CONCLUSION
So what to do to choose one of these products?
Our suggestion is obvious: inform yourself as best you can! Today, with the Internet, everything is easier, from consulting the software manufacturer to contacting groups of interested parties. An effort in this sense is the periodic organization of simulation meetings or workshops, bringing together the interested community. We also propose to maintain a website (www.coppead.ufrj.br/pesquisa/cel/po_simul.html) to assist in this exchange of information as part of the activities of the Simulation Nucleus of the Center for Studies in Logistics at COPPEAD/UFRJ . In this "site", in addition to providing several links, we will announce events in the area, provide articles, email list and maintain a discussion list about simulation. For this we count on the collaboration of all interested parties.
Links associated with simulation and simulation software
(For an up-to-date list, consult our “website” provided above)
MAIN INDICATIONS
• Informs College on Simulation (INFORMS/CS). INFORMS study group interested in simulation. Rich in information, with links to many software manufacturers. www.isye.gatech.edu/informs-sim
• SimTECH. Association of Simulation Software Manufacturers. Links to various manufacturers with brief descriptions of their products. www.sim-tech.org.
• Winter Simulation Conference. Main event in discrete event simulation, held annually in early December in the United States. In addition to the presence of specialists in the subject, the main simulation software manufacturers also exhibit their products. In 1997, it will be held between 07/12/97 and 10/12/97, in Atlanta. www.wintersim.org
OTHER INDICATIONS
• ACM Special Interest Group on Simulation (ACM/SIGSIM). www.acm.org/sigsim
• ACM Transaction on Modeling and Simulation (ACM/TOMACS). Electronic Journal. www.acm.org/pubs/tomacs
• Institute of Industrial Engineers (IIE). Publish magazine with ads, links and surveys. www.iienet.org
• Computer Simulation Modeling and Analysis (CSMA). Electronic Journal. tebbit.eng.umd.edu/simulation
• Michael Trick. Home Page rich in material about PO. mat.gsia.cmu.edu
• OR/MS Today. Magazine with ads, links and surveys. lionhrtpub.com/ORMS.html
• Palisade Corporation. Company that develops and sells various PO software, in particular @RISK and BestFit. www.palisade.com
• Society for Computer Simulation International (SCS). It publishes, among other things, a monthly magazine on simulation (Simulation). www.scs.org
BIBLIOGRAPHY
Banks, J. Interpreting Simulation Software Checklists, OR/MS Today, 22, 3, 74-78 (June 1996)
Banks, J. Software for Simulation. In Proceedings of the 1996 Winter Simulation Conference, Ed. JM Charnes, DJ Morrice, DT Brunner and JJ Swain, 31-38 (1996).
Banks, J. and Gibson, RR Selecting Simulation Software. IIE Solutions, 30-32 (May 1997)
Banks, J. and Gibson, RR Simulation Modeling: some programming required. IIE Solutions, 26-31 (February 1997)
Bard, J.F; deSilva, A; Bergevin, A. Evaluating Simulation Software for Postal Service Use: Technique Versus Perception. IEEE Transactions on Eng. Management, 44, 31-42 (1997).
Rodrigues Jr., JM 1995 Directory of Simulation Software. The Society for Computer Simulation, 1995.
Rohrer, M. Seeing the Importance of Visualization in Manufacturing Simulation. IIE Solutions, 24-28 (May 1997).
Saliby, E. SIMUL 3.1. Software and manual. COPPEAD/UFRJ, 1996.
Swain, JJ Flexible Tools for Modeling. OR/MS Today, 19, 62-74 (December 1993)
_____________. Simulation Software Buyers Guide. IIE Solutions, 56-67 (May 1995)
