normal_distribution 類別

產生常態分佈。

template<class RealType = double> class normal_distribution { public:     // types     typedef RealType result_type;     struct param_type;     // constructors and reset functions     explicit normal_distribution(RealType mean = 0.0, RealType stddev = 1.0);     explicit normal_distribution(const param_type& parm);     void reset();     // generating functions     template<class URNG>     result_type operator()(URNG& gen);     template<class URNG>     result_type operator()(URNG& gen, const param_type& parm);     // property functions     RealType mean() const;     RealType stddev() const;     param_type param() const;     void param(const param_type& parm);     result_type min() const;     result_type max() const; };

參數

• RealType
  浮點結果類型，預設值為 double。 如需可能的類型，請參閱 <random>。

備註

此範本類別描述產生使用者指定之整數類型的值的分佈 (若無提供則為 double 類型)，而這是根據常態分佈進行分佈。 下表提供各個成員的文章連結。

normal_distribution::normal_distribution	normal_distribution::mean	normal_distribution::param
normal_distribution::operator()	normal_distribution::stddev	normal_distribution::param_type

屬性函式 mean() 和 stddev() 會分別傳回儲存的分佈參數 mean 和 stddev 的值。

如需分佈類別及其成員的詳細資訊，請參閱 <random>。

如需常態分佈的詳細資訊，請參閱 Wolfram MathWorld 文章：常態分佈 (英文)。

範例

 

// 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);
}

輸出

Use CTRL-Z to bypass data entry and run using default values.
Enter a floating point value for the 'mean' distribution parameter: 0
Enter a floating point value for the 'stddev' distribution parameter (must be greater than zero): 1
Enter an integer value for the sample count: 10

min() == -1.79769e+308
max() == 1.79769e+308
m() == 0.0000000000
s() == 1.0000000000
Distribution for 10 samples:
          1:  -0.8845823965
          2:  -0.1995761116
          3:  -0.1162665130
          4:  -0.0685154932
          5:   0.0403741461
          6:   0.1591327792
          7:   1.0414389924
          8:   1.5876269426
          9:   1.6362637713
         10:   2.7821317338

需求

標頭：<random>

命名空間: std

請參閱

參考

<random>