std::normal_distribution (3) - Linux Manuals

std::normal_distribution: std::normal_distribution

NAME

std::normal_distribution - std::normal_distribution

Synopsis

Defined in header <random>
template< class RealType = double > (since C++11)
class normal_distribution;

Generates random numbers according to the Normal_(or_Gaussian)_random_number_distribution. It is defined as:

      f(x; μ,σ) =

      1
      σ
      √
      2π

      exp⎛
      ⎜
      ⎝

      -1
      2

      ⎛
      ⎜
      ⎝

      x-μ
      σ

      ⎞
      ⎟
      ⎠2
      ⎞
      ⎟
      ⎠

Here μ is the mean and 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 RealType
param_type the type of the parameter set, see RandomNumberDistribution.

Member functions

              constructs new distribution
constructor (public member function)
              resets the internal state of the distribution
reset (public member function)

Generation

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

Characteristics

              returns the distribution parameters
mean (public member function)
stddev
              gets or sets the distribution parameter object
param (public member function)
              returns the minimum potentially generated value
min (public member function)
              returns the maximum potentially generated value
max (public member function)

Non-member functions

           compares two distribution objects
operator== (function)
operator!=
           performs stream input and output on pseudo-random number distribution
operator<< (function template)
operator>>

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::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.