gamma_distribution 类

生成 gamma 分布。

template<class RealType = double> class gamma_distribution { public:     // types     typedef RealType result_type;     struct param_type;     // constructors and reset functions     explicit gamma_distribution(RealType alpha = 1.0, RealType beta = 1.0);     explicit gamma_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 alpha() const;     RealType beta() const;     param_type param() const;     void param(const param_type& parm);     result_type min() const;     result_type max() const; };

参数

• RealType
  浮点结果类型，默认为 double。 有关可能的类型，请参阅 <random>。

备注

如果未根据 Gamma 分布提供和分布任何类型，则模板类将描述产生用户指定的整型值或 double 型值的分布。 下表链接到有关各个成员的文章。

gamma_distribution::gamma_distribution	gamma_distribution::alpha	gamma_distribution::param
gamma_distribution::operator()	gamma_distribution::beta	gamma_distribution::param_type

属性函数 alpha() 和 beta() 返回存储的分布参数 alpha 和 beta 的各自值。

有关分布类及其成员的详细信息，请参阅 <random>。

有关 gamma 分布的详细信息，请参阅 Wolfram MathWorld 文章 Gamma 分布。

示例

 

// compile with: /EHsc /W4
#include <random> 
#include <iostream>
#include <iomanip>
#include <string>
#include <map>

void test(const double a, const double b, const int s) {

    // uncomment to use a non-deterministic generator
    //    std::random_device gen;

    std::mt19937 gen(1701);

    std::gamma_distribution<> distr(a, b);

    std::cout << std::endl;
    std::cout << "min() == " << distr.min() << std::endl;
    std::cout << "max() == " << distr.max() << std::endl;
    std::cout << "alpha() == " << std::fixed << std::setw(11) << std::setprecision(10) << distr.alpha() << std::endl;
    std::cout << "beta() == " << std::fixed << std::setw(11) << std::setprecision(10) << distr.beta() << std::endl;

    // generate the distribution as a histogram
    std::map<double, int> histogram;
    for (int i = 0; i < s; ++i) {
        ++histogram[distr(gen)];
    }

    // print results
    std::cout << "Distribution for " << s << " samples:" << std::endl;
    int counter = 0;
    for (const auto& elem : histogram) {
        std::cout << std::fixed << std::setw(11) << ++counter << ": "
            << std::setw(14) << std::setprecision(10) << elem.first << std::endl;
    }
    std::cout << std::endl;
}

int main()
{
    double a_dist = 0.0;
    double b_dist = 1;

    int samples = 10;

    std::cout << "Use CTRL-Z to bypass data entry and run using default values." << std::endl;
    std::cout << "Enter a floating point value for the 'alpha' distribution parameter (must be greater than zero): ";
    std::cin >> a_dist;
    std::cout << "Enter a floating point value for the 'beta' distribution parameter (must be greater than zero): ";
    std::cin >> b_dist;
    std::cout << "Enter an integer value for the sample count: ";
    std::cin >> samples;

    test(a_dist, b_dist, samples);
}

输出

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

min() == 4.94066e-324
max() == 1.79769e+308
alpha() == 1.0000000000
beta() == 1.0000000000
Distribution for 10 samples:
          1:   0.0936880533
          2:   0.1225944894
          3:   0.6443593183
          4:   0.6551171649
          5:   0.7313457551
          6:   0.7313557977
          7:   0.7590097389
          8:   1.4466885214
          9:   1.6434088411
         10:   2.1201210996

要求

标头：<random>

命名空间: std

请参见

参考

<random>