std::geometric_distribution
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: \(P(i|p) = p \cdot (1-p)^i\)P(i|p) = p · (1 − p)
iThe 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.
Template parameters
| IntType | - | The result type generated by the generator. The effect is undefined if this is not one of short, int, long, longlong, unsignedshort, unsignedint, unsignedlong, or unsignedlonglong. |
Member types
| Member type | Definition |
|---|---|
result_type (C++11) | IntType |
param_type (C++11) | the type of the parameter set, see RandomNumberDistribution. |
Member functions
|
(C++11) | constructs new distribution (public member function) |
|
(C++11) | resets the internal state of the distribution (public member function) |
Generation |
|
|
(C++11) | generates the next random number in the distribution (public member function) |
Characteristics |
|
|
(C++11) | returns the p distribution parameter (probability of a trial generating true) (public member function) |
|
(C++11) | gets or sets the distribution parameter object (public member function) |
|
(C++11) | returns the minimum potentially generated value (public member function) |
|
(C++11) | returns the maximum potentially generated value (public member function) |
Non-member functions
|
(C++11)(C++11)(removed in C++20) | compares two distribution objects (function) |
|
(C++11) | performs stream input and output on pseudo-random number distribution (function template) |
Example
std::geometric_distribution<>(0.5) is the default and represents the number of coin tosses that are required to get heads.
#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
External links
| Weisstein, Eric W. "Geometric Distribution." From MathWorld — A Wolfram Web Resource. |
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