Introducción a la simulación

PARTI P R I N C I P L E S

CHAPTER 1

P r i n c i p l e s

o f

S i m u l a t i o n

JERRY BANKS Georgia Institute of Technology

1.1

INTRODUCTION

The purpose of this handbook is to provide a reference to important topics that pertain to discrete-event simulation. All the contributors to this volume, who are a mix from academia, industry, and software developers, are highlyqualified. The book is intended for those who want to apply simulation to important problems. If you are new to simulation, reading this chapter will provide an overview to the remainder of the book. If you studied simulation several years ago, reading this chapter will provide a useful review and update. [Much of this introductory chapter is from Banks et al. (1995).] Chapter 1 is essentially inthree parts. The first part begins with a definition and an example of simulation. Then modeling concepts introduced in the example are presented. Four modeling structures for simulation are then presented. The second part of the chapter concerns subjective topics. First, the advantages and disadvantages of simulation are discussed. Then some of the areas of application are mentioned. Last, the stepsin the simulation process are described. The third part of the chapter has four sections. Each of these sections introduces operational aspects of discrete-event simulation. The chapter concludes with a summary.

1.2

DEFINITION OF SIMULATION

Simulation is the imitation of the operation of a real-world process or system over time. Simulation involves the generation of an artificial historyof the system and the observation of that artificial history to draw inferences concerning the operating characteristics of the real system that is represented. Simulation is an indispensable problemsolving methodology for the solution of many real-world problems. Simulation is used to describe and analyze the behavior of a system, ask what-if questions about the real
Handbook of Simulation,Edited by Jerry Banks.

ISBN 0-471-13403-1

© 1998 John Wiley & Sons, Inc.

system, and aid in the design of real systems. Both existing and conceptual systems can be modeled with simulation.

Example 1 (Ad Hoc Simulation) Consider the operation of a one-teller bank where customers arrive for service between 1 and 10 minutes apart in time, integer values only, each value equally likely. Thecustomers are served in between 1 and 6 minutes, also integer valued, and equally likely. Restricting the times to integer values is an abstraction of reality since time is continuous, but this aids in presenting the example. The objective is to simulate the bank operation, by hand, until 20 customers are served, and to compute measures of performance such as the percentage of idle time, theaverage waiting time per customer, and so on. Admittedly, 20 customers are far too few to draw conclusions about the operation of the system for the long run, but by following this example, the stage is set for further discussion in this chapter and subsequent discussion about using the computer for performing simulation. To simulate the process, random interarrival and service times need to begenerated. Assume that the interarrival times are generated using a spinner that has possibilities for the values 1 through 10. Further assume that the service times are generated using a die that has possibilities for the values 1 through 6. Table 1.1 is called an ad hoc simulation table. The setup of the simulation table is for
Table 1.1 Ad Hoc Simulation (1) (2) Time Between Arrivals 5 1 10 6 2 9 110 3 5 2 3 5 4 3 7 8 7 7 (3) Arrival Time 0 5 6 16 22 24 33 34 44 47 52 54 57 62 66 69 76 84 91 98 (4) Service Time 2 2 6 5 6 4 3 4 1 3 1 2 3 6 2 6 4 5 3 1 (5) Service Begins 0 5 7 16 22 28 33 36 44 47 52 54 57 62 68 70 76 84 91 98 (6) Time Service Ends 2 7 13 21 28 32 36 40 45 50 53 56 60 68 70 76 80 89 94 99 (7) Time in System 2 2 7 5 6 8 3 6 1 3 1 2 3 6 4 7 4 5 3 1 79 (8) Idle Time 0 3 0 3 1 0...