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In Memoriam: James O. Henriksen (1945–2019)
James O. Henriksen, one of the pioneers in the field of computer simulation, passed away on April 6, 2019. This commemoration of Jim summarizes his ground-breaking contributions to the development of software and methodology for simulation of complex systems as well as his service to WSC and the international simulation community.
Jim’s career in simulation began in 1967, when he joined The University of Michigan Computing Center (UMCC) and took over the maintenance and support of the GASP II, SIMSCRIPT II, and GPSS/360 simulation languages running under the Michigan Terminal System on an IBM 360/67 computer. He took Tom Schriber’s graduate course on simulation using GPSS in the spring of 1968, thus starting a collaboration and friendship that continued for 51 years. Subsequently Jim served in the US Army (1968–1970), where he applied his simulation expertise to top-secret analyses of the Safeguard Antiballistic Missile Program. Then he resumed his work with UMCC and Tom Schriber (1970–1974) before joining Consolidated Analysis Centers Inc. (CACI) to implement SIMSCRIPT II.5 on the Univac 1108 computer (1974–1975).
Jim founded Wolverine Software in 1976 to develop and market a new version of GPSS that would substantially outperform its competitors. In 1977 Jim introduced GPSS/H, which was the culmination of his ideas for performance improvement that he derived from his experiences with various simulation models running on different computers. Since that time Jim made landmark contributions to the area of simulation software design, implementation, and applications as exemplified by the following papers.
Henriksen, J. O. 1975. “Building a Better GPSS: A 3:1 Performance Enhancement.” In Proceedings of the 1975 Winter Simulation Conference, edited by O. S. Madrigal and R. Huntsinger, 465–469. La Jolla, California: Simulation Councils, Inc.
Henriksen, J. O. 1977a. “An Interactive Debugging Facility for GPSS.” In Proceedings of the 1977 Winter Simulation Conference, edited by H. J. Highland, R. G. Sargent, and J. W. Schmidt, 331–338. Piscataway, New Jersey: Institute of Electrical and Electronics Engineers.
Henriksen, J. O. 1983. “The Integrated Simulation Environment (Simulation Software of the 1990s).” Operations Research 31 (6): 1053–1073.
Brunner, D. T., and J. O. Henriksen. 1989. “A General Purpose Animator.” In Proceedings of the 1989 Winter Simulation Conference, edited by E. A. MacNair, K. J. Musselman, and P. Heidelberger, 155–163. Piscataway, New Jersey: Institute of Electrical and Electronics Engineers.
Henriksen, J. O. 1993. “SLX, The Successor to GPSS/H.” In Proceedings of the 1993 Winter Simulation Conference, edited by G. W. Evans, M. Mollaghasemi, E. C. Russell, and W. E. Biles, 263–268. Piscataway, New Jersey: Institute of Electrical and Electronics Engineers.
Earle, N. J., and J. O. Henriksen. 1994. “Proof Animation: Reaching New Heights in Animation.” In Proceedings of the 1994 Winter Simulation Conference, ed. J. D. Tew, S. Manivannan, D. A. Sadowski, and A. F. Seila, 509–516. Piscataway, New Jersey: Institute of Electrical and Electronics Engineers.
Henriksen, J. O. 2008. “Taming the Complexity Dragon.” Journal of Simulation 2:3–17.
In Henriksen (1975, 1977a), Jim documented the performance improvements delivered by GPSS/H versus competing versions of GPSS, especially with respect to interactive debugging facilities and the extraordinary increases in execution speed achieved by implementing the model translator as a compiler instead of an interpreter. In Henriksen (1983), Jim laid out a road map for advances in simulation software that would be needed in the future. With the development of SLX (Henriksen 1993, 2008) and Proof Animation (Brunner and Henriksen 1989, Earle and Henriksen 1994), Jim and his collaborators provided state-of-the-art software tools to meet those needs. SLX is an extensible general-purpose simulation language that enables users to implement new modeling and analysis facilities using the same tools that were used to develop baseline SLX. Proof Animation enabled users to create high-resolution two- and three-dimensional animations not only for simulations but also for a wide range of other applications.
In a remarkable series of papers on using simulation to solve complex problems, Jim laid a foundation for the art of simulation modeling as documented in the following paper and its references.
Henriksen, J. O. 1989. “Alternative Modeling Perspectives: Finding the Creative Spark.” In Proceedings of the 1989 Winter Simulation Conference, edited by E. A. MacNair, K. J. Musselman, and P. Heidelberger, 648–652. Piscataway, New Jersey: Institute of Electrical and Electronics Engineers.
Perhaps the most intriguing aspect of Jim’s technical work concerns the development of efficient algorithms for the management of simulation event lists. The following papers exemplify Jim’s seminal contributions in this area.
Henriksen, J. O. 1977b. “An Improved Events List Algorithm.” In Proceedings of the 1977 Winter Simulation Conference, edited by H. J. Highland, R. G. Sargent, and J. W. Schmidt, 547–557.
Henriksen, J. O. 2009. “Efficient Modeling of Delays in Discrete-Event Simulation.” In Advancing the Frontiers of Simulation: A Festschrift in Honor of George Samuel Fishman, edited by C. Alexopoulos, D. Goldsman, and J. R. Wilson, 105–141. New York: Springer Verlag.
It is noteworthy that in addition to the numerous short courses on simulation that he gave around the world, Jim taught simulation and other computer science courses as a Teaching Assistant at The University of Michigan and as an Adjunct Professor of Computer Science at Virginia Tech Northern Virginia Center. Jim also served WSC in several positions of great responsibility. While serving as the Business Chair for WSC 1981, he initiated the addition of the exhibits area, which was inaugurated in 1984. While serving as the General Chair for WSC 1986, he introduced a manufacturing track into the program, which was another major enhancement of the conference. During the period 1987–1990, Jim served on the Board of Directors as the representative of ACM/SIGSIM. For the Twenty-Fifth Anniversary WSC in 1992, Jim was one of four keynote speakers as documented in the WSC Proceedings paper.
Jim received the highest forms of recognition for his pioneering work in computer simulation. In 2006 he presented the WSC Titans of Simulation Plenary Address titled “Taming the Complexity Dragon,” See also Henriksen (2008). In 2013 he discussed all aspects of his career in a video-recorded interview with Prof. Dick Nance (Virginia Tech) for the Computer Simulation Archive at the North Carolina State University (NCSU) Libraries. In 2018 Jim received the Lifetime Professional Achievement Award from the INFORMS Simulation Society, which is the highest award given by that society for major contributions to the field of simulation.
Jim Henriksen’s professional achievements are remarkable not only for their impact on the field of simulation but also for length of time over which that impact was sustained in all its dimensions. We will continue to benefit from Jim’s work far into the future. Jim was a polymath in an age of hyperspecialization; an entrepreneur with an overriding concern for his employees’ personal and professional advancement; a humorist of penetrating insight; and above all, a man whose brilliance, patience, and kindness had an extraordinary effect on everyone whose life he touched. He will be greatly missed.
(Prepared by Jim Wilson)