geometric_distribution Class

The latest version of this topic can be found at geometric_distribution Class.

Generates a geometric distribution.

Syntax

class geometric_distribution {
public:    
    // types 
    typedef IntType result_type; 
    struct param_type;   
    // constructors and reset functions 
    explicit geometric_distribution(double p = 0.5);
    explicit geometric_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 p() const;
    param_type param() const;
    void param(const param_type& parm);
    result_type min() const;
    result_type max() const;
}; 

Parameters

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

Remarks

The template class describes a distribution that produces values of a user-specified integral type with a geometric distribution. The following table links to articles about individual members.

The property function p() returns the value for stored distribution parameter p.

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

For detailed information about the chi-squared distribution, see the Wolfram MathWorld article Geometric Distribution.

Example

// 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::geometric_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.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 << "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 = 0.5;  
  
    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 \'p\' distribution parameter: ";  
    std::cin >> p_dist;  
    std::cout << "Enter an integer value for the sample count: ";  
    std::cin >> samples;  
  
    test(p_dist, samples);  
}  
  

Output

First test:

Use CTRL-Z to bypass data entry and run using default values.Enter a floating point value for the 'p' distribution parameter: .5Enter an integer value for the sample count: 100min() == 0max() == 2147483647p() == 0.5000000000Distribution for 100 samples:    0 ::::::::::::::::::::::::::::::::::::::::::::::::::::    1 ::::::::::::::::::::::::    2 ::::::::::::::    3 :::::    4 ::    5 ::    6 :  

Second test:

Use CTRL-Z to bypass data entry and run using default values.Enter a floating point value for the 'p' distribution parameter: .1Enter an integer value for the sample count: 100min() == 0max() == 2147483647p() == 0.1000000000Distribution for 100 samples:    0 :::::::::    1 :::::::::::    2 :::::::    3 ::::::::    4 ::::::::    5 ::::::    6 :::::    7 ::::::    8 :::::    9 ::::   10 ::::   11 ::   12 :   13 :   14 :::   15 ::::   16 :::   17 :   18 :   19 :   20 ::   21 :   22 :   23 :   28 ::   33 :   35 :   40 :  

Requirements

Header: <random>

Namespace: std

geometric_distribution::geometric_distribution

Constructs the distribution.

explicit geometric_distribution(RealType p = 0.5);

 
explicit geometric_distribution(const param_type& parm);

Parameters

p
The p distribution parameter.

parm
The parameter structure used to construct the distribution.

Remarks

Precondition: 0.0 < p && p < 1.0

The first constructor constructs an object whose stored p value holds the value p.

The second constructor constructs an object whose stored parameters are initialized from parm. You can obtain and set the current parameters of an existing distribution by calling the param() member function.

geometric_distribution::param_type

Stores the parameters of the distribution.

struct param_type {
typedef geometric_distribution<IntType, RealType> distribution_type;
param_type(RealType p = 0.5); RealType p() const; .....
bool operator==(const param_type& right) const; bool operator!=(const param_type& right) const; };

Parameters

See parent topic geometric_distribution Class.

Remarks

Precondition: 0.0 < p && p < 1.0

This structure can be passed to the distribution's class constructor at instantiation, to the param() member function to set the stored parameters of an existing distribution, and to operator() to be used in place of the stored parameters.

See Also

<random>