Alan Pritsker's Multifaceted Career: Theory, Practice, Education, Entrepreneurship, and Service

IIE Transactions (2001) 33, 139±147 Alan Pritsker's multifaceted career: theory, practice, education, entrepreneurship, and service JAMES R. WILSON1 and DAVID GOLDSMAN2 1Department of Industrial Engineering, North Carolina State University, Raleigh, NC 27695-7906, USA E-mail: [email protected] 2School of Industrial and Systems Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0205, USA E-mail: [email protected] Received July 2000 and accepted July 2000 In this lead article for the special issue of IIE Transactions honoring Alan Pritsker, we summarize Alan's most signi®cant contributions to the ®elds of industrial engineering and operations research, with special emphasis on his contributions to computer simulation. 1. Introduction and games from the manufacturer to distribution centers and ®nally to retail stores. These applications and other Since he began his career as an industrial engineer over 45 aspects of Alan's career can be found in Alan's profes- years ago, Alan Pritsker made seminal contributions to sional autobiography Papers, Experiences, Perspectives many areas of the ®eld of simulation and to the larger (Pritsker, 1990). ®elds of industrial engineering and operations research. Particularly notable is the extent to which Alan's ac- complishments spanned both the theory and practice of 2. Contributions to engineering theory engineering and science ± Alan was always keenly inter- and methodology ested in bringing the latest research results quickly into practical applications for the bene®t of society at large. Foremost among Alan's achievements is his work in the From his pioneering work in developing theory and theory and methodology of discrete and combined dis- methodology for modeling and analysis of large-scale crete-continuous system simulation. industrial systems to his leadership in developing commercial simulation software products and in crafting 2.1. General modeling techniques policy analyses to address major societal problems, Alan's multifaceted contributions to the engineering profession With an eye towards applications, Alan and his students are striking not only for their scope and impact but also formulated the basic principles of combined discrete- for the remarkably long time period over which that im- continuous simulation and implemented those principles pact has been sustained in all its dimensions. in the GASP IV, SAINT, and SMOOTH simulation lan- Alan studied under Jack Mitten at The Ohio State guages (Hurst and Pritsker, 1973; Pritsker and Hurst, University, who taught him how to be a compassionate 1973; Pritsker, 1974a; Pritsker et al., 1974; Sigal and professor while pursuing research goals. Alan's research Pritsker, 1974). Subsequently Alan extended the foun- focus at the time was on the discrete control of stochastic dations of combined simulation to encompass the pro- processes, which he applied at the Battelle Memorial In- cess-interaction approach; and working with several stitute (now Battelle Institute) on such projects as un- collaborators, he implemented a family of combined dis- derstanding human-computer joint decision making, the crete-continuous simulation languages, including SLAM basis for automatic checkout techniques, and modeling (Pritsker and Pegden, 1979) and its extensions ± SLAM II railroading as a system. Alan's other projects at Battelle and SLAM II/PC (Pritsker, 1984a, 1986, 1995); TESS included: simulation of an air duel environment; the ap- (Standridge and Pritsker, 1987); SLAMSYSTEM (Prits- plication of the traveling salesman procedure to the wir- ker Corporation, 1989); FACTOR/AIM (Lilegdon et al., ing design of a computer; and development and use of a 1994); and Visual SLAM/AweSim (Pritsker et al., 1997; mathematical model of the supply-chain network for toys Pritsker and O'Reilly, 1999). Alan's pioneering work on 0740-817X Ó 2001 `ÌIE'' 140 Wilson and Goldsman combined simulation forms the basis for virtually all of intractability of stochastic networks with more general the major combined simulation languages in use today. node and arc characteristics prompted Alan to develop the Q-GERT simulation language (Pritsker, 1977, 1979) as a vehicle for analyzing general stochastic networks. Of 2.2. General analysis techniques equal interest is the work of Alan, Elliott Sigal, and Jim Alan made numerous fundamental contributions to Solberg on the stochastic shortest route problem, in- general simulation analysis techniques in the following cluding graph-theoretic constructs such as uniformly di- areas: the spectral method for output analysis (Duket rected cutsets that enable eective use of the Monte Carlo and Pritsker, 1978); the simulation start-up problem method of conditional expectations for simulation-based (Wilson and Pritsker, 1978a, b); variance reduction analysis of this problem (Sigal et al., 1979, 1980). This techniques for the simulation of queueing systems (Wil- work has stimulated substantial follow-up research in son and Pritsker, 1984a, b); and analytic characteriza- graph theory as well as in simulation. tions of the transient and steady-state behavior of the variance of the sample mean for simulated Markov 2.4. Commercial simulation software systems processes in discrete and continuous time (Hazen and Pritsker, 1980). Although much of this work was done in Since the late 1960s, Alan has perhaps become most the 1970s and early 1980s, it is still frequently cited in the widely known for leading the development of a series of current literature. In 1985, Wilson and Pritsker (1984b) highly successful software systems designed to support all received the `Òutstanding Simulation Publication aspects of a large-scale simulation study. Alan made Award'' from The Institute of Management Sciences simulation `èasy to use.'' As President of Pritsker & (TIMS, now INFORMS) College on Simulation and Associates, Inc. (later Pritsker Corporation and then the Gaming (now the College on Simulation, or INFORMS± Pritsker Division of Symix Systems, Inc.), Alan super- CS). Alan's most recent research was focused on: (i) the vised the design and implementation of the following formulation of practical, ecient statistical screening, commercial simulation software systems: selection, and multiple-comparison procedures that are · GASP II simulation language (Pritsker and Kiviat, adapted to large-scale system simulation; and (ii) the 1969). implementation of these procedures in commercial sim- · GERTE program for analyzing GERT networks ulation software (Goldsman et al., 1999). Professor Barry (Pritsker, 1974b). Nelson of Northwestern University described his work · GASP IV simulation language (Hurst and Pritsker, with Alan on this topic as follows. 1973; Pritsker and Hurst, 1973; Pritsker, 1974a). Over the past three years, Alan (via Pritsker Corporation) was a · SAINT simulation language (Pritsker et al., 1974). co-sponsor of one of my National Science Foundation grants on · GASP_PL/I simulation language (Pritsker and comparing systems via simulation. I originally envisioned the role of the corporate sponsors of this work as directing my eorts Young, 1975). toward practical problems and implementing research results in · Q-GERT simulation language (Pritsker, 1977, 1979). their software. But in very short order, Alan became a participant · SLAM, SLAM II, and SLAM II/PC simulation in the research itself, despite the fact he had no previous experience languages (Pritsker and Pegden, 1979; Pritsker, in the types of multiple-comparison procedures I derive. As usual, 1984a, 1986, 1995). he provided insights and directions that would never have occurred to me. · TESS simulation environment (Standridge and Pritsker, 1987). · SLAMSYSTEM simulation environment (Pritsker 2.3. Modeling and analysis of stochastic networks Corporation, 1989). · FACTOR/AIM manufacturing simulation environ- Alan's contributions to techniques for modeling, analysis, ment (Pritsker et al., 1986; Lilegdon et al., 1994). and simulation of stochastic networks deserve special · Visual SLAM simulation language and AweSim mention. The Graphical Evaluation and Review Tech- simulation environment (Pritsker et al., 1997; Prits- nique (GERT) was a breakthrough that provided a ker and O'Reilly, 1999). method to calculate the moment-generating function of the accumulated time (or cost) to realize a stochastic It is also noteworthy that the Micro Saint software network composed of `èxclusive-or'' nodes and arcs package currently distributed by Micro Analysis and whose traversal times (costs) are independent random Design, Inc., is a direct descendant of the original SAINT variables (Pritsker and Happ, 1966; Pritsker and White- package developed by Alan and his collaborators house, 1966; Whitehouse and Pritsker, 1969). For (Pritsker et al., 1974) for the US Government. this work Alan and Gary Whitehouse received the The Extended Simulation Support System (TESS) ``H. B. Maynard Innovative Achievement in Industrial was one of the ®rst comprehensive simulation Engineering Award'' from the American Institute of In- `ènvironments'' for speci®cation, development, veri®ca- dustrial Engineers (AIIE, now IIE) in 1978. The analytic tion, validation, documentation, management, anima- Alan Pritsker's multifaceted career 141 tion, and presentation of simulation models (Standridge June 18, 1998, Alan testi®ed in Congressional Hearings and Pritsker, 1987). In parallel with his work on simu- on the results of his comparison of the current liver-al- lation-oriented environments, Alan (working with David

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