std::normal_distribution

From cppreference.com

Defined in header `<random>`

template< class RealType = double > class normal_distribution;		(since C++11)

Normal (or Guassian) random number distribution:

f(x; μ,σ) = 1 σ \sqrt 2π exp ⎛ ⎜ ⎝ - 12 ⎛ ⎜ ⎝ x-μ σ ⎞ ⎟ ⎠ 2 ⎞ ⎟ ⎠

With the mean $μ$ and the standard deviation (stddev) $σ$ .


(constructor)	constructs new distribution (public member function)

reset	resets the internal state of the distribution (public member function)
Generation

operator()	generates the next random number in the distribution (public member function)
Characteristics

mean	returns the mean ( $μ$ ) distribution parameter (public member function)

stddev	returns the standard deviation ( $σ$ ) distribution parameter (public member function)

param	gets or sets the distribution parameter object (public member function)

min	returns the minimum potentially generated value (public member function)

max	returns the maximum potentially generated value (public member function)

[edit] Non-member functions


operator== operator!=	compares two distribution objects (function)

operator<< operator>>	performs stream input and output on pseudo-random number distribution (function)

[edit] Example

run this code

#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

[edit] External links

Weisstein, Eric W. "Normal Distribution." From MathWorld--A Wolfram Web Resource.
Normal Distribution. From Wikipedia.

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)


Member type	Definition

`result_type`	RealType

`param_type`	the type of the parameter set, unspecified

std::normal_distribution

Contents

[edit] Member types

[edit] Member functions

Generation

Characteristics

[edit] Non-member functions

[edit] Example

[edit] External links