std::lognormal_distribution
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lognormal_distribution
(C++11)
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std::lognormal_distribution
Member functions
Generation
Characteristics
Non-member functions
(C++11)(C++11)(until C++20)
(C++11)(C++11)
Defined in header
<random>
template< class RealType = double >
class lognormal_distribution;
(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) = 1sx√2 πexp⎛
⎜
⎝-(ln x - m)22s2⎞
⎟
⎠
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
[edit] Member functions
Generation
Characteristics
[edit] Non-member functions
(C++11)
(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.