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@dc1394
Created December 31, 2023 13:09
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Twitterのモンテカルロ法のC++版の速度比較コード(C++に備え付けのrand())
#include <cstdlib> // for std::rand, std::srand
#include <iomanip> // for std::setprecision
#include <ios> // for std::ios::fixed, std::ios::floatfield
#include <iostream> // for std::cout, std::endl
namespace {
inline double mcpi();
}
int main()
{
std::cout.setf(std::ios::fixed, std::ios::floatfield);
std::cout << "pi = "
<< std::setprecision(16)
<< mcpi()
<< std::endl;
}
namespace {
double mcpi()
{
auto constexpr seed = 20231226;
auto constexpr num_points = 1000000000;
auto num_inside = 0;
std::srand(seed);
for (auto i = 0; i < num_points; i++) {
auto const x = static_cast<double>(std::rand()) / static_cast<double>(RAND_MAX);
auto const y = static_cast<double>(std::rand()) / static_cast<double>(RAND_MAX);
auto const r2 = x * x + y * y;
if (r2 < 1.0) {
num_inside++;
}
}
return 4.0 * static_cast<double>(num_inside) / static_cast<double>(num_points);
}
}
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