std::binomial_distribution

 

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std::binomial_distribution

Member functions

binomial_distribution::binomial_distribution

binomial_distribution::reset

Generation

binomial_distribution::operator()

Characteristics

binomial_distribution::p

binomial_distribution::t

binomial_distribution::param

binomial_distribution::min

binomial_distribution::max

Non-member functions

operator== operator!=

operator<< operator>>

 

Defined in header <random>
template< class IntType = int > class binomial_distribution;		(since C++11)

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

P(i|t,p) =⎛
⎜
⎝t
p⎞
⎟
⎠ · pi
· (1 − p)t−i

The value obtained is the number of successes in a sequence of t yes/no experiments, each of which succeeds with probability p.

Member types

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

Member functions

(constructor)	constructs new distribution (public member function)
reset	resets the internal state of the distribution (public member function)
Generation
operator()	generates the next random number in the distribution (public member function)
Characteristics
t	returns the t distribution parameter (number of trials) (public member function)
p	returns the p distribution parameter (probability of a trial generating true) (public member function)
param	gets or sets the distribution parameter object (public member function)
min	returns the minimum potentially generated value (public member function)
max	returns the maximum potentially generated value (public member function)

Non-member functions

operator== operator!=	compares two distribution objects (function)
operator<< operator>>	performs stream input and output on pseudo-random number distribution (function)

Example

plot of binomial distribution with probability of success of each trial exactly 0.5, illustrating the relationship with the pascal triangle (the probabilities that none, 1, 2, 3, or all four of the 4 trials will be successful in this case are 1:4:6:4:1)

#include <iostream>
#include <iomanip>
#include <string>
#include <map>
#include <random>
int main()
{
    std::random_device rd;
    std::mt19937 gen(rd());
    // perform 4 trials, each succeeds 1 in 2 times
    std::binomial_distribution<> d(4, 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 ******

External links

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