std::geometric_distribution
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geometric_distribution
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std::geometric_distribution
Member functions
Generation
Characteristics
Non-member functions
(C++11)(C++11)(until C++20)
(C++11)(C++11)
Defined in header
<random>
template< class IntType = int >
class geometric_distribution;
(since C++11)
class geometric_distribution;
Produces random non-negative integer values i, distributed according to discrete probability function:
- \(P(i|p) = p \cdot (1-p)^i\)P(i|p) = p · (1 − p)i
The value represents the number of failures in a series of independent yes/no trials (each succeeds with probability p), before exactly 1 success occurs.
std::geometric_distribution<>(p) is exactly equivalent to std::negative_binomial_distribution <>(1, p). It is also the discrete counterpart of std::exponential_distribution .
std::geometric_distribution satisfies RandomNumberDistribution.
Contents
[edit] Template parameters
IntType
-
The result type generated by the generator. The effect is undefined if this is not one of short, int, long, long long, unsigned short, unsigned int, unsigned long, or unsigned long long.
[edit] Member types
Member type
Definition
result_type (C++11)
IntType
[edit] Member functions
Generation
Characteristics
(C++11)
(public member function) [edit]
[edit] Non-member functions
(C++11)
(function template) [edit]
[edit] Example
std::geometric_distribution<>(0.5) is the default and represents the number of coin tosses that are required to get heads.
Run this code
#include <iomanip> #include <iostream> #include <map> #include <random> #include <string> 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 [x, y] : hist) { const char c = x < 10 ? x + '0' : x - 10 + 'a'; std::cout << c << ' ' << std::string (y / 100, '*') << '\n'; } }
Possible output:
0 ************************************************* 1 ************************* 2 ************ 3 ****** 4 ** 5 * 6 7 8 9
[edit] External links
Weisstein, Eric W. "Geometric Distribution." From MathWorld — A Wolfram Web Resource.