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

From cppreference.com
< cpp‎ | numeric‎ | random
(corrected the meaning of m,s (cmp example below and wikipedia))
(Added Wikipedia link to Log-normal distribution)
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The lognormal_distribution random number distribution produces random numbers {{math|x > 0}} according to a log-normal distribution:
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The lognormal_distribution random number distribution produces random numbers {{math|x > 0}} according to a log-normal distribution:
  
 
:{{math|f(x; m,s) {{=}} {{mfrac||1|sx{{mrad|2 π}} }} exp{{mparen|(|)|- {{mfrac||(ln x - m){{su|p=2}}| 2s{{su|p=2}}}} }} }}
 
:{{math|f(x; m,s) {{=}} {{mfrac||1|sx{{mrad|2 π}} }} exp{{mparen|(|)|- {{mfrac||(ln x - m){{su|p=2}}| 2s{{su|p=2}}}} }} }}

Revision as of 22:01, 8 June 2018

 
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 Template:concept

Contents

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 (C++11) the type of the parameter set, see RandomNumberDistribution.

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]

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]

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

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/numeric/random/lognormal_distribution&oldid=102396"