Alignment Properties in Ordinal Comparison of DiscreteEvent Dynamic Systems

  • Authors:
  • Liyi Dai;Jeffrey E. Wieselthier

  • Affiliations:
  • Department of Systems Science and Mathematics, Washington University, St. Louis, Missouri 63130-4899;Information Technology Division, Naval Research Laboratory, Washington, DC 20375

  • Venue:
  • Discrete Event Dynamic Systems
  • Year:
  • 1999

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Abstract

In the design and optimizationof discrete event dynamic systems, it is often necessary to orderalternative designs based on their relative performance, i.e.,to rank them from best to worst. In this paper, alignment ofobserved performance orders with true orders is considered andproperties of the alignment are investigated. Spearman‘s rankcorrelation coefficient is a measure of agreement between theobserved performance orders and the true ones. It is shown thatSpearman‘s coefficient converges exponentially in the simulationtime or observation time, which gives a strong evidence of theefficiency of order comparison for discrete event dynamic systems.In the context of simulation, the effect of simulation dependenceon the alignment is also discussed. It is found that neitherindependent simulation nor the scheme of common random numbers(CRN), a popular scheme for variance reduction, can yield dominantperformance. Finally, numerical examples based on a networkingoptimization problem are provided to illustrate the convergenceof Spearman‘s coefficient. In these examples, the standard clock(SC) simulation technique provides much faster convergence thaneither independent simulations or CRN simulations. Both the SCand CRN methods use the same random number sequence to drivemany events in parallel; however, under SC the events drivingthe parallel experiments are all identical, whereas under CRNthey may be different.