4.17_montecarlo.c

/*
 * Name     : Tri Wanda Septian
 * 
 * How to compile the source codes (Linux)
 * $gcc -pthread -o outputfile sourcecode.c
 * 
 * 4.17*: An interesting way of calculating phi is to use a technique known as Monte Carlo, which involves randomization. 
 * This technique works as follows: Suppose you have a circle inscribed within a square, as shown in Figure 4.18. 
 * (Assume that the radius of this circle is 1.)
 * 
 * First, generate a series of random points as simple (x,y) coordinates. 
 * These points must fall within the Cartesian coordinates that bound the square. Of the total number of random points that are generated, some will occur within the circle.
 * Next, estimate phi by performing the following calculation:
 * phi =4*(number of points in circle)/(total number of points)
 * Write a multithreaded version of this algorithm that creates a separate thread to generate a number of random points.
 * The thread will count the number of points that occur within the circle and store the result in a global variable.
 * When this thread has exited, the parent thread will calculate and output the estimated value of phi. 
 */

#include<stdio.h>
#include<string.h>
#include<pthread.h>
#include<stdlib.h>

int i = 0; //loop counter
int count = 0; //count holds all the number of how many good coordinates
double x,y; //x,y value for thre random coordinate
double z; //used to check if x*x+y*y <=1
int totalpoints;

void *runner(void *param){

    /*initialize random numbers*/
    for (i= 0; i < totalpoints; ++i){

        x = (double)rand() / RAND_MAX; /*generate random x coordinate number*/
        y = (double)rand() / RAND_MAX; /*generate random y coordinate number*/

        z = x*x+y*y;
        if ( z <= 1){
            count++;
        }
    }
    pthread_exit(0);
}

int main(int argc, char *argv[]){

    printf("\nWelcome to Thread Process with Monte Carlo Technique\n");

    srand((unsigned int) time(NULL));
    pthread_t thread; // the thread identifier


    if(argc !=2 ){
        fprintf(stderr,"\nUsage : montecarlo.out <integer value>\n");
        return -1;
    }
    if (atoi(argv[1]) < 0){
        fprintf(stderr,"%d must be >= 0\n",atoi(argv[1]));
        return -1;
    }

    int numberIter = atoi(argv[1]); //number if iterations per FOR LOPP
    totalpoints = numberIter;

    pthread_create(&thread,NULL,&runner, NULL); //create the thread
    pthread_join(thread,NULL);//wait forthre thread to exit

    double phi = 4*((double)count/(double)totalpoints); //phi calculation formula
    printf("\nNumber of Iteration = %d , estimate of phi is %g \n",totalpoints,phi);

    return 0;

}