NAME¶

std::lognormal_distribution - std::lognormal_distribution

Synopsis¶

Defined in header <random>
template< class RealType = double > (since C++11)
class lognormal_distribution;

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 long double.

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 constructs new distribution
(C++11) (public member function)
reset resets the internal state of the distribution
(C++11) (public member function)

Generation¶

operator() generates the next random number in the distribution
(C++11) (public member function)

Characteristics¶

m returns the distribution parameters
s (public member function)
(C++11)
param gets or sets the distribution parameter object
(C++11) (public member function)
min returns the minimum potentially generated value
(C++11) (public member function)
max returns the maximum potentially generated value
(C++11) (public member function)

Non-member functions¶

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