std::lognormal_distribution

 

C++

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Pseudo-random number generation

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Random number distributions Uniform distributions uniform_int_distribution (C++11) uniform_real_distribution (C++11) generate_canonical (C++11) Bernoulli distributions bernoulli_distribution (C++11) binomial_distribution (C++11) negative_binomial_distribution (C++11) geometric_distribution (C++11) Poisson distributions poisson_distribution (C++11) exponential_distribution (C++11) gamma_distribution (C++11) weibull_distribution (C++11) extreme_value_distribution (C++11) Normal distributions normal_distribution (C++11) lognormal_distribution (C++11) chi_squared_distribution (C++11) cauchy_distribution (C++11) fisher_f_distribution (C++11) student_t_distribution (C++11) Sampling distributions discrete_distribution (C++11) piecewise_constant_distribution (C++11) piecewise_linear_distribution (C++11)

 

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!= (C++11)(C++11)(until C++20)

operator<<operator>> (C++11)(C++11)

 

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:

\({\small f(x;m,s) = \frac{1}{sx\sqrt{2\pi} } \exp{(-\frac{ {(\ln{x} - m)}^{2} }{2{s}^{2} })} }\)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.

Template parameters

RealType

-

The result type generated by the generator. The effect is undefined if this is not one of float, double, or longdouble.

Member types

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

Member functions

(constructor) (C++11)	constructs new distribution (public member function)
reset (C++11)	resets the internal state of the distribution (public member function)
Generation
operator() (C++11)	generates the next random number in the distribution (public member function)
Characteristics
ms (C++11)	returns the distribution parameters (public member function)
param (C++11)	gets or sets the distribution parameter object (public member function)
min (C++11)	returns the minimum potentially generated value (public member function)
max (C++11)	returns the maximum potentially generated value (public member function)

Non-member functions

operator==operator!= (C++11)(C++11)(removed in C++20)	compares two distribution objects (function)
operator<<operator>> (C++11)	performs stream input and output on pseudo-random number distribution (function template)

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

External links

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