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

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< cpp‎ | numeric‎ | random
m
m (PI -> π)
Line 8: Line 8:
 
The lognormal_distribution random number distribution produces random numbers {{math|x > 0}} according to a log-normal distribution:
 
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 PI}} }} exp{{mparen|(|)|- {{mfrac||(ln x - m){{su|p=2}}| 2s{{su|p=2}}}} }} }}
+
:{{math|f(x; m,s) {{=}} {{mfrac||1|sx{{mrad|2 }} }} exp{{mparen|(|)|- {{mfrac||(ln x - m){{su|p=2}}| 2s{{su|p=2}}}} }} }}
  
 
The parameter {{math|m}} is the mean and the parameter {{math|s}} the standard deviation.
 
The parameter {{math|m}} is the mean and the parameter {{math|s}} the standard deviation.

Revision as of 02:59, 14 July 2012

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

Contents

Member types

Member type Definition
result_type RealType
param_type the type of the parameter set, unspecified

Member functions

Template:cpp/numeric/random/distribution/dcl list constructorTemplate:cpp/numeric/random/distribution/dcl list resetTemplate:cpp/numeric/random/distribution/dcl list operator()Template:cpp/numeric/random/lognormal distribution/dcl list mTemplate:cpp/numeric/random/lognormal distribution/dcl list sTemplate:cpp/numeric/random/distribution/dcl list paramTemplate:cpp/numeric/random/distribution/dcl list minTemplate:cpp/numeric/random/distribution/dcl list max
Generation
Characteristics

Non-member functions

Template:cpp/numeric/random/distribution/dcl list operator cmpTemplate:cpp/numeric/random/distribution/dcl list operator ltltgtgt

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

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