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std::geometric_distribution

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Pseudo-random number generation
Engines and engine adaptors
Generators
Distributions
Uniform distributions
Bernoulli distributions
geometric_distribution
(C++11)
Poisson distributions
Normal distributions
Sampling distributions
Seed Sequences
(C++11)
C library
 
 
Defined in header <random>
template< class IntType = int >
class geometric_distribution;
(since C++11)

Produces random non-negative integer values i, distributed according to discrete probability function:

P(i|p) = p · (1 − p)i

The value represents the number of yes/no trials (each succeeding with probability p) which are necessary to obtain a single success.

std::geometric_distribution<>(p) is exactly equivalent to std::negative_binomial_distribution<>(1, p). It is also the discrete counterpart of std::exponential_distribution.

Contents

Member types

Member type Definition
result_type IntType
param_type the type of the parameter set, unspecified

Member functions

Template:cpp/numeric/random/distribution/dcl list constructorTemplate:cpp/numeric/random/distribution/dcl list resetTemplate:cpp/numeric/random/distribution/dcl list operator()Template:cpp/numeric/random/geometric distribution/dcl list pTemplate:cpp/numeric/random/distribution/dcl list paramTemplate:cpp/numeric/random/distribution/dcl list minTemplate:cpp/numeric/random/distribution/dcl list max
Generation
Characteristics

Non-member functions

Template:cpp/numeric/random/distribution/dcl list operator cmpTemplate:cpp/numeric/random/distribution/dcl list operator ltltgtgt

Example

geometric_distribution<>(0.5) is the default and represents the number of coin tosses that are required to get heads

#include <iostream>
#include <iomanip>
#include <string>
#include <map>
#include <random>
int main()
{
    std::random_device rd;
    std::mt19937 gen(rd());
 
    std::geometric_distribution<> d; // same as std::negative_binomial_distribution<> d(1, 0.5);
 
    std::map<int, int> hist;
    for(int n=0; n<10000; ++n) {
        ++hist[d(gen)];
    }
    for(auto p : hist) {
        std::cout << p.first <<
                ' ' << std::string(p.second/100, '*') << '\n';
    }
}

Output:

0 *************************************************
1 *************************
2 ************
3 ******
4 **
5 *
6 
7 
8 
9 
10 
11

External links

Weisstein, Eric W. "Geometric Distribution." From MathWorld--A Wolfram Web Resource.