std:: poisson_distribution
From cppreference.com
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Defined in header
<random>
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||
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template
<
class
IntType
=
int
>
class poisson_distribution ; |
(since C++11) | |
Produces random non-negative integer values i , distributed according to discrete probability function:
-
P(i|μ) =
e -μ ·μ i i!
The value obtained is the probability of exactly i occurrences of a random event if the expected, mean number of its occurrence under the same conditions (on the same time/space interval) is μ .
std::poisson_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 , long long , unsigned short , unsigned int , unsigned long , or unsigned long long . |
Member types
| Member type | Definition |
result_type
(C++11)
|
IntType
|
param_type
(C++11)
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the type of the parameter set, see RandomNumberDistribution . |
Member functions
|
(C++11)
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constructs new distribution
(public member function) |
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(C++11)
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resets the internal state of the distribution
(public member function) |
Generation |
|
|
(C++11)
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generates the next random number in the distribution
(public member function) |
Characteristics |
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(C++11)
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returns the
mean
distribution parameter (mean number of occurrences of the event)
(public member function) |
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(C++11)
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gets or sets the distribution parameter object
(public member function) |
|
(C++11)
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returns the minimum potentially generated value
(public member function) |
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(C++11)
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returns the maximum potentially generated value
(public member function) |
Non-member functions
|
(C++11)
(C++11)
(removed in C++20)
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compares two distribution objects
(function) |
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(C++11)
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performs stream input and output on pseudo-random number distribution
(function template) |
Example
Run this code
#include <iomanip> #include <iostream> #include <map> #include <random> #include <string> int main() { std::random_device rd; std::mt19937 gen(rd()); // If an event occurs 4 times a minute on average, how // often is it that it occurs n times in one minute? std::poisson_distribution<> d(4); std::map<int, int> hist; for (int n = 0; n != 10000; ++n) ++hist[d(gen)]; for (auto [x, y] : hist) std::cout << std::hex << x << ' ' << std::string(y / 100, '*') << '\n'; }
Possible output:
0 * 1 ******* 2 ************** 3 ******************* 4 ******************* 5 *************** 6 ********** 7 ***** 8 ** 9 * a b c d
External links
| Weisstein, Eric W. "Poisson Distribution." From MathWorld — A Wolfram Web Resource. |