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: f(x; μ,σ) =
| 1 |
| σ√2π |
| -1 |
| 2 |
| x-μ |
| σ |
Here μ is the mean and σ is the standard deviation (stddev).
std::normal_distribution satisfies all requirements of RandomNumberDistribution.
| RealType | - | The result type generated by the generator. The effect is undefined if this is not one of float, double, or long double. |
| Member type | Definition |
|---|---|
result_type | RealType |
param_type | the type of the parameter set, see RandomNumberDistribution. |
| 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) |
|
| compares two distribution objects (function) |
|
| performs stream input and output on pseudo-random number distribution (function template) |
#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::fixed << std::setprecision(1) << std::setw(2)
<< p.first << ' ' << std::string(p.second/200, '*') << '\n';
}
}Output:
-2 -1 0 1 * 2 *** 3 ****** 4 ******** 5 ********** 6 ******** 7 ***** 8 *** 9 * 10 11 12
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