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negative_binomial_distribution Class

Generates a negative binomial distribution.

template<class IntType = int>
class negative_binomial_distribution
{
public:
    // types
    typedef IntType result_type;
    struct param_type;
    // constructor and reset functions
    explicit negative_binomial_distribution(IntType k = 1, double p = 0.5);
    explicit negative_binomial_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
    IntType k() const;
    double p() const;
    param_type param() const;
    void param(const param_type& parm);
    result_type min() const;
    result_type max() const;
};

IntType

The integer result type, defaults to int. For possible types, see <random>.

The template class describes a distribution that produces values of a user-specified integral type, or type int if none is provided, distributed according to the Negative Binomial Distribution discrete probability function. The following table links to articles about individual members.

negative_binomial_distribution::negative_binomial_distribution

negative_binomial_distribution::k

negative_binomial_distribution::param

negative_binomial_distribution::operator()

negative_binomial_distribution::p

negative_binomial_distribution::param_type

The property members k() and p() return the currently stored distribution parameter values k and p respectively.

For more information about distribution classes and their members, see <random>.

For detailed information about the negative binomial distribution discrete probability function, see the Wolfram MathWorld article Negative Binomial Distribution.

 

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

void test(const int k, const double p, const int& s) {

    // uncomment to use a non-deterministic seed
    //    std::random_device rd;
    //    std::mt19937 gen(rd());
    std::mt19937 gen(1729);

    std::negative_binomial_distribution<> distr(k, p);

    std::cout << std::endl;
    std::cout << "k == " << distr.k() << std::endl;
    std::cout << "p == " << distr.p() << 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 << "Histogram 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()
{
    int    k_dist = 1;
    double p_dist = 0.5;
    int    samples = 100;

    std::cout << "Use CTRL-Z to bypass data entry and run using default values." << std::endl;
    std::cout << "Enter an integer value for k distribution (where 0 < k): ";
    std::cin >> k_dist;
    std::cout << "Enter a double value for p distribution (where 0.0 < p <= 1.0): ";
    std::cin >> p_dist;
    std::cout << "Enter an integer value for a sample count: ";
    std::cin >> samples;

    test(k_dist, p_dist, samples);
}

First run:

Use CTRL-Z to bypass data entry and run using default values.
Enter an integer value for k distribution (where 0 < k): 1
Enter a double value for p distribution (where 0.0 < p <= 1.0): .5
Enter an integer value for a sample count: 100

k == 1
p == 0.5
Histogram for 100 samples:
    0 :::::::::::::::::::::::::::::::::::::::::::
    1 ::::::::::::::::::::::::::::::::
    2 ::::::::::::
    3 :::::::
    4 ::::
    5 ::

Second run:

Use CTRL-Z to bypass data entry and run using default values.
Enter an integer value for k distribution (where 0 < k): 100
Enter a double value for p distribution (where 0.0 < p <= 1.0): .667
Enter an integer value for a sample count: 100

k == 100
p == 0.667
Histogram for 100 samples:
   31 ::
   32 :
   33 ::
   34 :
   35 ::
   37 ::
   38 :
   39 :
   40 ::
   41 :::
   42 :::
   43 :::::
   44 :::::
   45 ::::
   46 ::::::
   47 ::::::::
   48 :::
   49 :::
   50 :::::::::
   51 :::::::
   52 ::
   53 :::
   54 :::::
   56 ::::
   58 :
   59 :::::
   60 ::
   61 :
   62 ::
   64 :
   69 ::::

Header: <random>

Namespace: std

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