std::lognormal_distribution

 

C++

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Technical Specifications

 

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normal_distribution (C++11)

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C library

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std::lognormal_distribution

Member functions

lognormal_distribution::lognormal_distribution

lognormal_distribution::reset

Generation

lognormal_distribution::operator()

Characteristics

lognormal_distribution::mlognormal_distribution::s

lognormal_distribution::param

lognormal_distribution::min

lognormal_distribution::max

Non-member functions

operator==operator!=

operator<<operator>>

 

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

sx√2 π

exp⎛
⎜
⎝-

(ln x - m)2

2s2

⎞
⎟
⎠

The parameter m is the mean and the parameter s the standard deviation.

std::lognormal_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

(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
ms	returns the distribution parameters (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)

Non-member functions

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

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());
 
    std::lognormal_distribution<> d(1.6, 0.25);
 
    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 
 3 ***
 4 *************
 5 ***************
 6 *********
 7 ****
 8 *
 9 
10 
11 
12

External links

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