poisson_distribution 类
生成泊松分布。
template<class IntType = int> class poisson_distribution { public: // types typedef IntType result_type; struct param_type; // constructors and reset functions explicit poisson_distribution(double mean = 1.0); explicit poisson_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 double mean() const; param_type param() const; void param(const param_type& parm); result_type min() const; result_type max() const; };
参数
- IntType
整数结果类型,默认为 int。 有关可能的类型,请参阅 <random>。
备注
模板类将描述使用泊松分布产生用户指定的整型值的分布。 下表链接到有关各个成员的文章。
poisson_distribution::mean |
poisson_distribution::param |
|
poisson_distribution::operator() |
属性函数 mean() 将返回存储的分布参数 mean 的值。
有关分布类及其成员的详细信息,请参阅 <random>。
有关泊松分布的详细信息,请参阅 Wolfram MathWorld 文章泊松分布。
示例
// compile with: /EHsc /W4
#include <random>
#include <iostream>
#include <iomanip>
#include <string>
#include <map>
void test(const double p, const int s) {
// uncomment to use a non-deterministic generator
// std::random_device gen;
std::mt19937 gen(1701);
std::poisson_distribution<> distr(p);
std::cout << std::endl;
std::cout << "min() == " << distr.min() << std::endl;
std::cout << "max() == " << distr.max() << std::endl;
std::cout << "p() == " << std::fixed << std::setw(11) << std::setprecision(10) << distr.mean() << std::endl;
// generate the distribution as a histogram
std::map<int, int> histogram;
for (int i = 0; i < s; ++i) {
++histogram[distr(gen)];
}
// print results
std::cout << "Distribution for " << s << " samples:" << std::endl;
for (const auto& elem : histogram) {
std::cout << std::setw(5) << elem.first << ' ' << std::string(elem.second, ':') << std::endl;
}
std::cout << std::endl;
}
int main()
{
double p_dist = 1.0;
int samples = 100;
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 'mean' distribution parameter (must be greater than zero): ";
std::cin >> p_dist;
std::cout << "Enter an integer value for the sample count: ";
std::cin >> samples;
test(p_dist, samples);
}
输出
首次测试:
第二次测试:
要求
标头:<random>
命名空间: std