49
edits
Changes
→Examples
== Examples ==
<source lang="cpp">
// Workshop 2 - Calculate PI by integrating 1/(1+x^2)
// w2.serial.cpp
#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <chrono>
#include <omp.h>
using namespace std::chrono;
// report system time
//
void reportTime(const char* msg, steady_clock::duration span) {
auto ms = duration_cast<milliseconds>(span);
std::cout << msg << " - took - " <<
ms.count() << " milliseconds" << std::endl;
}
int main(int argc, char** argv) {
if (argc != 2) {
std::cerr << argv[0] << ": invalid number of arguments\n";
std::cerr << "Usage: " << argv[0] << " no_of_slices\n";
return 1;
}
int i;
int nthreads;
int n = std::atoi(argv[1]);
int mnt = omp_get_max_threads();
steady_clock::time_point ts, te;
double sum = 0.0; // scalar accumulator
// calculate pi by integrating the area under 1/(1 + x^2) in n steps
double pi = 0.0;
double stepSize = 1.0 / (double)n;
ts = steady_clock::now();
#pragma omp parallel
{
int i, tid, nt;
double x, psum;
tid = omp_get_thread_num();
nt = omp_get_num_threads();
if (tid == 0) nthreads = nt;
for (i = tid, psum = 0.0; i < n; i += nt) {
x = ((double)i + 0.5) * stepSize;
psum += 1.0 / (1.0 + x * x);
}
#pragma omp critical
sum += psum;
}
pi = 4.0 * sum * stepSize;
te = steady_clock::now();
std::cout << "n = " << n << "\n" <<
mnt << " threads available\n" <<
nthreads << " threads used.\nTime = " <<
std::fixed << std::setprecision(15) <<
"\n pi(exact) = " << 3.141592653589793 <<
"\n pi(calcd) = " << pi << std::endl;
reportTime("Integration", te - ts);
}
</source>
= Intel Advisor Tutorial Example =
