/* -------------------------------------------------------------------------  * This program is a next-event simulation of a single-server FIFO service * node using Exponentially distributed interarrival times and Erlang  * distributed service times (i.e., a M/E/1 queue).  The service node is  * assumed to be initially idle, no arrivals are permitted after the  * terminal time STOP, and the node is then purged by processing any  * remaining jobs in the service node. * * Name            : ssq4.c  (Single Server Queue, version 4) * Author          : Steve Park & Dave Geyer * Language        : ANSI C * Latest Revision : 11-09-98 * -------------------------------------------------------------------------  */#include <stdio.h>#include <math.h>#include "rngs.h"                      /* the multi-stream generator */#include "rvgs.h"                      /* random variate generators  */#define START         0.0              /* initial time                   */#define STOP      20000.0              /* terminal (close the door) time */#define INFINITY   (100.0 * STOP)      /* must be much larger than STOP  */   double Min(double a, double c)/* ------------------------------ * return the smaller of a, b * ------------------------------ */{   if (a < c)    return (a);  else    return (c);}    double GetArrival()/* --------------------------------------------- * generate the next arrival time, with rate 1/2 * --------------------------------------------- */ {  static double arrival = START;  SelectStream(0);   arrival += Exponential(2.0);  return (arrival);}    double GetService()/* -------------------------------------------- * generate the next service time with rate 2/3 * -------------------------------------------- */ {  SelectStream(1);  return (Erlang(5, 0.3));}     int main(void){  struct {    double arrival;                 /* next arrival time                   */    double completion;              /* next completion time                */    double current;                 /* current time                        */    double next;                    /* next (most imminent) event time     */    double last;                    /* last arrival time                   */  } t;  struct {    double node;                    /* time integrated number in the node  */    double queue;                   /* time integrated number in the queue */    double service;                 /* time integrated number in service   */  } area      = {0.0, 0.0, 0.0};  long index  = 0;                  /* used to count departed jobs         */  long number = 0;                  /* number in the node                  */  PlantSeeds(0);  t.current    = START;           /* set the clock                         */  t.arrival    = GetArrival();    /* schedule the first arrival            */  t.completion = INFINITY;        /* the first event can't be a completion */  while ((t.arrival < STOP) || (number > 0)) {    t.next          = Min(t.arrival, t.completion);  /* next event time   */    if (number > 0)  {                               /* update integrals  */      area.node    += (t.next - t.current) * number;      area.queue   += (t.next - t.current) * (number - 1);      area.service += (t.next - t.current);    }    t.current       = t.next;                    /* advance the clock */    if (t.current == t.arrival)  {               /* process an arrival */      number++;      t.arrival     = GetArrival();      if (t.arrival > STOP)  {        t.last      = t.current;        t.arrival   = INFINITY;      }      if (number == 1)        t.completion = t.current + GetService();    }    else {                                        /* process a completion */      index++;      number--;      if (number > 0)        t.completion = t.current + GetService();      else        t.completion = INFINITY;    }  }   printf("\nfor %ld jobs\n", index);  printf("   average interarrival time = %6.2f\n", t.last / index);  printf("   average wait ............ = %6.2f\n", area.node / index);  printf("   average delay ........... = %6.2f\n", area.queue / index);  printf("   average service time .... = %6.2f\n", area.service / index);  printf("   average # in the node ... = %6.2f\n", area.node / t.current);  printf("   average # in the queue .. = %6.2f\n", area.queue / t.current);  printf("   utilization ............. = %6.2f\n", area.service / t.current);  return (0);}