std::normal_distribution
Defined in header <random> |
||
|---|---|---|
template< class RealType = double > class normal_distribution; |
(since C++11) |
Generates random numbers according to the Normal (or Gaussian) random number distribution. It is defined as: \(\small{f(x;\mu,\sigma)}=\frac{1}{\sigma\sqrt{2\pi} }\exp{(-\frac{1}{2}{(\frac{x-\mu}{\sigma})}^2)}\)f(x; μ,σ) =
1/σ√2π exp ⎛⎜
⎝-1/2 ⎛
⎜
⎝x-μ/σ⎞
⎟
⎠2
⎞
⎟
⎠
Here \(\small\mu\)μ is the mean and \(\small\sigma\)σ is the standard deviation (stddev).
std::normal_distribution satisfies all requirements of RandomNumberDistribution.
Template parameters
| RealType | - | The result type generated by the generator. The effect is undefined if this is not one of float, double, or long double. |
Member types
| Member type | Definition |
|---|---|
result_type(C++11) |
RealType |
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 |
|
| returns the distribution parameters (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
#include <iostream>
#include <iomanip>
#include <string>
#include <map>
#include <random>
#include <cmath>
int main()
{
std::random_device rd{};
std::mt19937 gen{rd()};
// values near the mean are the most likely
// standard deviation affects the dispersion of generated values from the mean
std::normal_distribution<> d{5,2};
std::map<int, int> hist{};
for(int n=0; n<10000; ++n) {
++hist[std::round(d(gen))];
}
for(auto p : hist) {
std::cout << std::setw(2)
<< p.first << ' ' << std::string(p.second/200, '*') << '\n';
}
}
Possible output:
-2 -1 0 1 * 2 *** 3 ****** 4 ******** 5 ********** 6 ******** 7 ***** 8 *** 9 * 10 11 12
External links
- Weisstein, Eric W. "Normal Distribution." From MathWorld--A Wolfram Web Resource.
- Normal Distribution. From Wikipedia.
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