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exercise3_solution.c
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exercise3_solution.c
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/* =================================================================
monte-carlo-pi-openmp.c
Written by Frederick Fung for NCI OpenMP Workshop March 2022
This program approximates the pi value by Monte-Carlo method.
The code is accelerated by openmp multi-threading.
Compile: gcc -fopenmp -g -Wall -O3 -lm -o monte-carlo-pi-openmp monte-carlo-pi-openmp.c
Usage: ./monte-carlo-pi-openmp
.....................................................................
Produced for NCI Training.
Frederick Fung 2022
4527FD1D
====================================================================*/
#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#include<omp.h>
#include<math.h>
#define MATH_PI acos(-1.0)
void calc_pi(int *hit, int *samples ){
double x = 0;
double y = 0;
long i;
int count =0;
double start = omp_get_wtime();
#pragma omp parallel private(x, y, i )
{
unsigned int seed = omp_get_thread_num()+123;
#pragma omp for reduction(+:count)
for (i=0; i<*samples; i++){
x = rand_r(&seed)/ (double) RAND_MAX;
y = rand_r(&seed)/ (double) RAND_MAX;
if (x*x + y*y <= 1.0f) count+=1;
}
} // end of openmp
double end = omp_get_wtime();
printf("openmp walltime %f seconds\n ", end - start);
*hit = count;
}
int main ()
{ int trials[]={10,100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000};
printf("MATH Pi %f\n", MATH_PI);
printf("/////////////////////////////////////////////////////\n" );
for (int i = 0; i< sizeof(trials) / sizeof(trials[0]); i++){
int samples = trials[i];
int hit;
hit = 0;
calc_pi(&hit, &samples);
printf("Sampling points %d; Hit numbers %d; Approx Pi %f\n", samples, hit, (double) hit/ samples * 4.0f);
}
return 0;
}