std::lognormal_distribution
Defined in header <random> |
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|---|---|---|
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 long double. |
Member types
| Member type | Definition |
|---|---|
result_type |
RealType |
param_type(C++11) |
the type of the parameter set, see RandomNumberDistribution. |
Member functions
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(C++11)
|
constructs new distribution (public member function) |
|
(C++11)
|
resets the internal state of the distribution (public member function) |
Generation |
|
|
(C++11)
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generates the next random number in the distribution (public member function) |
Characteristics |
|
| returns the distribution parameters (public member function) |
|
|
(C++11)
|
gets or sets the distribution parameter object (public member function) |
|
(C++11)
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returns the minimum potentially generated value (public member function) |
|
(C++11)
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returns the maximum potentially generated value (public member function) |
Non-member functions
|
(C++11)(C++11)(removed in C++20)
|
compares two distribution objects (function) |
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(C++11)
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performs stream input and output on pseudo-random number distribution (function template) |
Example
#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';
}
}
Possible output:
2 3 *** 4 ************* 5 *************** 6 ********* 7 **** 8 * 9 10 11 12
External links
- Weisstein, Eric W. "Log Normal Distribution." From MathWorld--A Wolfram Web Resource.
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