12 Simulation Classes

12.1 Process Classes

TBD

12.2 Resource Classes

TBD

12.3 Example—Simulation Classes

This example is the same as Example 3 in Chapter 8 Data Collection. Since this example uses classes, the racket language is required instead of the racket/base language.

#lang scheme

;  Example 4 - Classes

(require (planet williams/simulation/simulation-with-graphics))

(define n-attendants 2)

(define attendant #f)

(define-process-class generator%

(init-field (n 1000))

(do ((i 0 (+ i 1)))

((= i n) (void))

(wait (random-exponential 4.0))

(make-object customer% i)))

(define-process-class customer%

(init-field i)

(begin

(send attendant request)

(work (random-flat 2.0 10.0))

(send attendant relinquish)))

(define (run-simulation n)

(with-new-simulation-environment

(set! attendant (make-object resource% n-attendants))

(make-object generator% n)

(accumulate (variable-statistics (send attendant queue-variable-n)))

(accumulate (variable-history (send attendant queue-variable-n)))

(start-simulation)

(printf "--- Example 4 - Classes ---~n")

(printf "Maximum queue length = ~a~n"

(variable-maximum (send attendant queue-variable-n)))

(printf "Average queue length = ~a~n"

(variable-mean (send attendant queue-variable-n)))

(printf "Variance             = ~a~n"

(variable-variance (send attendant queue-variable-n)))

(printf "Utilization          = ~a~n"

(variable-mean (send attendant satisfied-variable-n)))

(printf "Variance             = ~a~n"

(variable-variance (send attendant satisfied-variable-n)))

(printf "~a~n" (history-plot (variable-history

(send attendant queue-variable-n))))))

(run-simulation 1000)

The output is identical to the example in Section 8.3 Example—Data Collection (except for the heading).

--- Example 4 - Classes ---

Maximum queue length = 8

Average queue length = 0.9120534884951139

Variance             = 2.2420855874934826

Utilization          = 1.4320511974417858

Variance             = 0.5885107114317054