| 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.
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 | the type of the parameter set, see RandomNumberDistribution. |
Member functions
| constructs new distribution (public member function) | |
| resets the internal state of the distribution (public member function) | |
Generation | |
| operator()
| generates the next random number in the distribution (public member function) |
Characteristics | |
| returns the distribution parameters (public member function) | |
| gets or sets the distribution parameter object (public member function) | |
| returns the minimum potentially generated value (public member function) | |
| returns the maximum potentially generated value (public member function) | |
Non-member functions
| compares two distribution objects (function) | |
| 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';
}
}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.
- Log-normal distribution. From Wikipedia.
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