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/* External definitions for inventory system. */
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "lcgrand.h" /* Header file for random-number generator. */
int amount, bigs, initial_inv_level, inv_level, next_event_type, num_events,
    num_months, num_values_demand, smalls;
float area_holding, area_shortage, holding_cost, incremental_cost, maxlag,
    mean_interdemand, minlag, prob_distrib_demand[26], setup_cost,
    shortage_cost, sim_time, time_last_event, time_next_event[5],
    total_ordering_cost;
FILE *infile, *outfile;
void initialize(void);
void timing(void);
void order_arrival(void);
void demand(void);
void evaluate(void);
void report(void);
void update_time_avg_stats(void);
float expon(float mean);
int random_integer(float prob_distrib[]);
float uniform(float a, float b);

int main() /* Main function. */
{
  int i, num_policies;
  /* Open input and output files. */
  infile = fopen("in.txt", "r");
  outfile = fopen("out.txt", "w");
  /* Specify the number of events for the timing function. */
  num_events = 4;
  /* Read input parameters. */
  fscanf(infile, "%d %d %d %d %f %f %f %f %f %f %f",
         &initial_inv_level, &num_months, &num_policies, &num_values_demand,
         &mean_interdemand, &setup_cost, &incremental_cost, &holding_cost,
         &shortage_cost, &minlag, &maxlag);
  for (i = 1; i <= num_values_demand; ++i)
    fscanf(infile, "%f", &prob_distrib_demand[i]);
  /* Write report heading and input parameters. */
  fprintf(outfile, "------Single-product inventory system------\n\n");
  fprintf(outfile, "Initial inventory level: %d items\n\n",
          initial_inv_level);
  fprintf(outfile, "Number of demand sizes: %d\n\n", num_values_demand);
  fprintf(outfile, "Distribution function of demand sizes:");
  for (i = 1; i <= num_values_demand; ++i)
    fprintf(outfile, " %.2f", prob_distrib_demand[i]);
  fprintf(outfile, "\n\nMean inter-demand time: %.2f months\n\n", mean_interdemand);
  fprintf(outfile, "Delivery lag range: %.2f to %.2f months\n\n", minlag,
          maxlag);
  fprintf(outfile, "Length of simulation: %d months\n\n", num_months);
  fprintf(outfile, "Costs:\nK = %.2f\ni = %.2f\nh = %.2f\npi = %.2f\n\n",
          setup_cost, incremental_cost, holding_cost, shortage_cost);
  fprintf(outfile, "Number of policies: %d\n\n", num_policies);
  fprintf(outfile, "Policies:\n");
  fprintf(outfile, "--------------------------------------------------------------------------------------------------\n");
  fprintf(outfile, " Policy        Avg_total_cost     Avg_ordering_cost      Avg_holding_cost     Avg_shortage_cost\n");
  fprintf(outfile, "--------------------------------------------------------------------------------------------------");
  /* Run the simulation varying the inventory policy. */
  for (i = 1; i <= num_policies; ++i)
  {
    /* Read the inventory policy, and initialize the simulation. */
    fscanf(infile, "%d %d", &smalls, &bigs);
    initialize();
    /* Run the simulation until it terminates after an end-simulation event
       (type 3) occurs. */
    do
    {
      /* Determine the next event. */
      timing();
      /* Update time-average statistical accumulators. */
      update_time_avg_stats();
      /* Invoke the appropriate event function. */
      switch (next_event_type)
      {
      case 1:
        order_arrival();
        break;
      case 2:
        demand();
        break;
      case 4:
        evaluate();
        break;
      case 3:
        report();
        break;
      }
      /* If the event just executed was not the end-simulation event (type 3),
         continue simulating. Otherwise, end the simulation for the current
         (s,S) pair and go on to the next pair (if any). */
    } while (next_event_type != 3);
  }
  fprintf(outfile, "\n\n--------------------------------------------------------------------------------------------------");
  /* End the simulations. */
  fclose(infile);
  fclose(outfile);
  return 0;
}

void initialize(void) /* Initialization function. */
{                     /* Initialize the simulation clock. */
  sim_time = 0.0;
  /* Initialize the state variables. */
  inv_level = initial_inv_level;
  time_last_event = 0.0;
  /* Initialize the statistical counters. */
  total_ordering_cost = 0.0;
  area_holding = 0.0;
  area_shortage = 0.0;
  /* Initialize the event list. Since no order is outstanding, the order-
     arrival event is eliminated from consideration. */
  time_next_event[1] = 1.0e+30;
  time_next_event[2] = sim_time + expon(mean_interdemand);
  time_next_event[3] = num_months;
  time_next_event[4] = 0.0;
}

void timing(void) /* Timing function. */
{
  int i;
  float min_time_next_event = 1.0e+29;
  next_event_type = 0;
  /* Determine the event type of the next event to occur. */
  for (i = 1; i <= num_events; ++i)
    if (time_next_event[i] < min_time_next_event)
    {
      min_time_next_event = time_next_event[i];
      next_event_type = i;
    }
  /* Check to see whether the event list is empty. */
  if (next_event_type == 0)
  {
    /* The event list is empty, so stop the simulation. */
    fprintf(outfile, "\nEvent list empty at time %f", sim_time);
    exit(1);
  }
  /* The event list is not empty, so advance the simulation clock. */
  sim_time = min_time_next_event;
}

void order_arrival(void) /* Order arrival event function. */
{                        /* Increment the inventory level by the amount ordered. */
  inv_level += amount;
  /* Since no order is now outstanding, eliminate the order-arrival event from
     consideration. */
  time_next_event[1] = 1.0e+30;
}

void demand(void) /* Demand event function. */
{                 /* Decrement the inventory level by a generated demand size. */
  inv_level -= random_integer(prob_distrib_demand);
  /* Schedule the time of the next demand. */
  time_next_event[2] = sim_time + expon(mean_interdemand);
}

void evaluate(void) /* Inventory-evaluation event function. */
{                   /* Check whether the inventory level is less than smalls. */
  if (inv_level < smalls)
  {
    /* The inventory level is less than smalls, so place an order for the
       appropriate amount. */
    amount = bigs - inv_level;
    total_ordering_cost += setup_cost + incremental_cost * amount;
    /* Schedule the arrival of the order. */
    time_next_event[1] = sim_time + uniform(minlag, maxlag);
  }
  /* Regardless of the place-order decision, schedule the next inventory
     evaluation. */
  time_next_event[4] = sim_time + 1.0;
}

void report(void) /* Report generator function. */
{                 /* Compute and write estimates of desired measures of performance. */
  float avg_holding_cost, avg_ordering_cost, avg_shortage_cost;
  avg_ordering_cost = total_ordering_cost / num_months;
  avg_holding_cost = holding_cost * area_holding / num_months;
  avg_shortage_cost = shortage_cost * area_shortage / num_months;
  fprintf(outfile, "\n\n(%d,%3d)%20.2f%20.2f%20.2f%20.2f",
          smalls, bigs,
          avg_ordering_cost + avg_holding_cost + avg_shortage_cost,
          avg_ordering_cost, avg_holding_cost, avg_shortage_cost);
}

void update_time_avg_stats(void) /* Update area accumulators for time-average
                                    statistics. */
{
  float time_since_last_event;
  /* Compute time since last event, and update last-event-time marker. */
  time_since_last_event = sim_time - time_last_event;
  time_last_event = sim_time;
  /* Determine the status of the inventory level during the previous interval.
     If the inventory level during the previous interval was negative, update
     area_shortage. If it was positive, update area_holding. If it was zero,
     no update is needed. */
  if (inv_level < 0)
    area_shortage -= inv_level * time_since_last_event;
  else if (inv_level > 0)
    area_holding += inv_level * time_since_last_event;
}

float expon(float mean) /* Exponential variate generation function. */
{                       /* Return an exponential random variate with mean "mean". */
  return -mean * log(lcgrand(1));
}

int random_integer(float prob_distrib[]) /* Random integer generation
                                            function. */
{
  int i;
  float u;
  /* Generate a U(0,1) random variate. */
  u = lcgrand(1);
  /* Return a random integer in accordance with the (cumulative) distribution
     function prob_distrib. */
  for (i = 1; u >= prob_distrib[i]; ++i)
    ;
  return i;
}

float uniform(float a, float b) /* Uniform variate generation function. */
{                               /* Return a U(a,b) random variate. */
  return a + lcgrand(1) * (b - a);
}

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