std::normal_distribution
From cppreference.com
| Defined in header <random>
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||
template< class RealType = double >
class normal_distribution;
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(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; ,) =
exp1 2 -1 2 x-
2
Here \(\small\mu\) is the Mean and \(\small\sigma\) 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
|
the type of the parameter set, see RandomNumberDistribution. |
Member functions
| constructs new distribution (public member function) | |
| resets the internal state of the distribution (public member function) | |
Generation | |
| generates the next random number in the distribution (public member function) | |
Characteristics | |
| returns the distribution parameters (public member function) | |
| gets or sets the distribution parameter object (public member function) | |
| returns the minimum potentially generated value (public member function) | |
| 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
Run this code
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <random>
#include <string>
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{5.0, 2.0};
// Draw a sample from the normal distribution and round it to an integer.
auto random_int = [&d, &gen]{ return std::lround(d(gen)); };
std::map<long, unsigned> histogram{};
for (auto n{10000}; n; --n)
++histogram[random_int()];
for (const auto [k, v] : histogram)
std::cout << std::setw(2) << k << ' ' << std::string(v / 200, '*') << '\n';
}
Possible output:
-1
0
1 *
2 ***
3 *****
4 ********
5 *********
6 *********
7 ******
8 ***
9 *
10
11
External links
| 1. | Weisstein, Eric W. "Normal Distribution." From MathWorld A Wolfram Web Resource. |
| 2. | Normal distribution From Wikipedia. |