本文主要說明C++可以使用機率中的 Probability Distribution Function (PDF),不會對這些理論做說明,請自行研究機率理論。要舉的例子為常態分布。因為MSDN上有現成的例子,所以筆者直接引用 :
// compile with: /EHsc /W4
#include <random>
#include <iostream>
#include <iomanip>
#include <string>
#include <map>
using namespace std;
void test(const double m, const double s, const int samples) {
// uncomment to use a non-deterministic seed
// random_device gen;
// mt19937 gen(rd());
mt19937 gen(1701);
normal_distribution<> distr(m, s);
cout << endl;
cout << "min() == " << distr.min() << endl;
cout << "max() == " << distr.max() << endl;
cout << "m() == " << fixed << setw(11) << setprecision(10) << distr.mean() << endl;
cout << "s() == " << fixed << setw(11) << setprecision(10) << distr.stddev() << endl;
// generate the distribution as a histogram
map<double, int> histogram;
for (int i = 0; i < samples; ++i) {
++histogram[distr(gen)];
}
// print results
cout << "Distribution for " << samples << " samples:" << endl;
int counter = 0;
for (const auto& elem : histogram) {
cout << fixed << setw(11) << ++counter << ": "
<< setw(14) << setprecision(10) << elem.first << endl;
}
cout << endl;
}
int main()
{
double m_dist = 1;
double s_dist = 1;
int samples = 10;
cout << "Use CTRL-Z to bypass data entry and run using default values." << endl;
cout << "Enter a floating point value for the 'mean' distribution parameter: ";
cin >> m_dist;
cout << "Enter a floating point value for the 'stddev' distribution parameter (must be greater than zero): ";
cin >> s_dist;
cout << "Enter an integer value for the sample count: ";
cin >> samples;
test(m_dist, s_dist, samples);
}
除了常態分佈外,從MSDN可查到其他的分佈函數說明:https://msdn.microsoft.com/en-us/library/bb982398.aspx#distributions。
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