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Mon, Aug 5, 16:42
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Wed, Aug 7, 16:42 (2 d)
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rSCINTROPAR Introduction to parallelism
pi.cc
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/*
This exercise is taken from the class Parallel Programming Workshop (MPI,
OpenMP and Advanced Topics) at HLRS given by Rolf Rabenseifner
*/
#include <chrono>
#include <cstdio>
#include <cmath>
#ifdef _OPENMP
#include <omp.h>
#endif
using clk = std::chrono::high_resolution_clock;
using second = std::chrono::duration<double>;
using time_point = std::chrono::time_point<clk>;
inline int digit(double x, int n) {
return std::trunc(x * std::pow(10., n)) - std::trunc(x * std::pow(10., n - 1)) *10.;
}
inline double f(double a) { return (4. / (1. + a * a)); }
const int n = 10000000;
int main(int /* argc */ , char ** /* argv */) {
int i;
double dx, x, sum, pi;
int nthreads;
#ifdef _OPENMP
auto omp_t1 = omp_get_wtime();
#endif
auto t1 = clk::now();
/* calculate pi = integral [0..1] 4 / (1 + x**2) dx */
dx = 1. / n;
sum = 0.0;
for (i = 1; i <= n; i++) {
x = (1. * i - 0.5) * dx;
sum = sum + f(x);
}
pi = dx * sum;
#ifdef _OPENMP
auto omp_elapsed = omp_get_wtime() - omp_t1;
#endif
second elapsed = clk::now() - t1;
std::printf("computed pi = %.16g\n", pi);
#ifdef _OPENMP
std::printf("wall clock time (omp_get_wtime) = %.4gs in %d threads\n", omp_elapsed, nthreads);
#endif
std::printf("wall clock time (chrono) = %.4gs\n", elapsed.count());
for(int d = 1; d <= 15; ++d) {
std::printf("%d", digit(pi, d));
}
return 0;
}
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