std::binomial_distribution

From cppreference.com

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 ⎞ ⎟ ⎠ \cdot p i \cdot (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 $p$ .


(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)

[edit] Non-member functions


operator== operator!=	compares two distribution objects (function)

operator<< operator>>	performs stream input and output on pseudo-random number distribution (function)

[edit] 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)

run this code

#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';
    }
}

Possible output:

0 ******
1 ************************
2 *************************************
3 *************************
4 ******

[edit] External links

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

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)


Member type	Definition

`result_type`	IntType

`param_type`	the type of the parameter set, unspecified

std::binomial_distribution

Contents

[edit] Member types

[edit] Member functions

Generation

Characteristics

[edit] Non-member functions

[edit] Example

[edit] External links