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Difference between revisions of "cpp/numeric/random/lognormal distribution"

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template< class RealType = double >
 
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class lognormal_distribution;
 
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Latest revision as of 06:21, 2 May 2023

 
C++
 
Numerics library
 
Pseudo-random number generation
 
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
sx√2 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

(C++11)
 constructs new distribution
(public member function) [edit]
(C++11)
 resets the internal state of the distribution
(public member function) [edit]
Generation
(C++11)
 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]
(C++11)
 performs stream input and output on pseudo-random number distribution
(function template) [edit]

[edit] Example

Run this code
#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.
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/numeric/random/lognormal_distribution&oldid=151295"