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std::lognormal_distribution

From cppreference.com
< cpp‎ | numeric‎ | random
 
 
 
 
std::lognormal_distribution
 
Defined in header <random>
template< class RealType = double >
class lognormal_distribution;
(since C++11)

The lognormal_distribution random number distribution produces random numbers x > 0 according to a Log-normal distribution:

f(x; m,s) =
1
sx2 π
exp

-
(ln x - m)2
2s2


The parameters m and s are, respectively, the mean and standard deviation of the natural logarithm of x.

std::lognormal_distribution satisfies all requirements of RandomNumberDistribution.

Contents

[edit] 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.

[edit] Member types

Member type Definition
result_type (C++11) RealType
param_type (C++11) the type of the parameter set, see RandomNumberDistribution.

[edit] Member functions

constructs new distribution
(public member function) [edit]
(C++11)
resets the internal state of the distribution
(public member function) [edit]
Generation
generates the next random number in the distribution
(public member function) [edit]
Characteristics
(C++11)
returns the distribution parameters
(public member function) [edit]
(C++11)
gets or sets the distribution parameter object
(public member function) [edit]
(C++11)
returns the minimum potentially generated value
(public member function) [edit]
(C++11)
returns the maximum potentially generated value
(public member function) [edit]

[edit] Non-member functions

(C++11)(C++11)(removed in C++20)
compares two distribution objects
(function) [edit]
performs stream input and output on pseudo-random number distribution
(function template) [edit]

[edit] Example

#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <random>
#include <string>
 
int main()
{
    std::random_device rd;
    std::mt19937 gen(rd());
 
    std::lognormal_distribution<> d(1.6, 0.25);
 
    std::map<int, int> hist;
    for (int n = 0; n < 1e4; ++n)
        ++hist[std::round(d(gen))];
 
    for (std::cout << std::fixed << std::setprecision(1); auto [x, y] : hist)
        std::cout << std::hex << x << ' ' << std::string(y / 200, '*') << '\n';
}

Possible output:

2
3 ***
4 *************
5 ***************
6 *********
7 ****
8 *
9
a
b
c

[edit] External links

Weisstein, Eric W. "Log Normal Distribution." From MathWorld — A Wolfram Web Resource.