std::normal_distribution

template <class RealType = double> class normal_distribution;

Normal distribution

Random number distribution that produces floating-point values according to a normal distribution, which is described by the following probability density function:

 

This distribution produces random numbers around the distribution mean (μ) with a specific standard deviation (σ).

The normal distribution is a common distribution used for many kind of processes, since it is the distribution that the aggregation of a large number of independent random variables approximates to, when all follow the same distribution (no matter which distribution).

The distribution parameters, mean (μ) and stddev (σ), are set on construction.

To produce a random value following this distribution, call its member function operator().

Template parameters

RealType

A floating-point type. Aliased as member type  result_type.
By default, this is  double.

 

Member types

The following aliases are member types of normal_distribution:

member type	definition	notes
result_type	The first template parameter (RealType)	The type of the numbers generated (defaults to double)
param_type	not specified	The type returned by member param.

 

Member functions

(constructor)

Construct normal distribution  (public member function)

operator()

Generate random number  (public member function)

reset

Reset distribution  (public member function)

param

Distribution parameters  (public member function)

min

Minimum value  (public member function )

max

Maximum value  (public member function )

 

Distribution parameters:

normal_distribution::mean

Distribution mean  (public member function)

normal_distribution::stddev

Standard deviation  (public member function)

 

Non-member functions

operator<<

Insert into output stream  (function template )

operator>>

Extract from input stream  (function template )

relational operators

Relational operators  (function template )

 

Example

   

 1 // normal_distribution

 2 #include <iostream>

 3 #include <random>

 4 

 5 int main()

 6 {

 7   const int nrolls=10000;  // number of experiments

 8   const int nstars=100;    // maximum number of stars to distribute

 9 

10   std::default_random_engine generator;

11   std::normal_distribution<double> distribution(5.0,2.0);

12 

13   int p[10]={};

14 

15   for (int i=0; i<nrolls; ++i) {

16     double number = distribution(generator);

17     if ((number>=0.0)&&(number<10.0)) ++p[int(number)];

18   }

19 

20   std::cout << "normal_distribution (5.0,2.0):" << std::endl;

21 

22   for (int i=0; i<10; ++i) {

23     std::cout << i << "-" << (i+1) << ": ";

24     std::cout << std::string(p[i]*nstars/nrolls,'*') << std::endl;

25   }

26 

27   return 0;

28 }

Possible output:

normal_distribution (5.0,2.0): 0-1: * 1-2: **** 2-3: ********* 3-4: *************** 4-5: ****************** 5-6: ******************* 6-7: *************** 7-8: ******** 8-9: **** 9-10: *