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⎛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.
| RealType | - | The result type generated by the generator. The effect is undefined if this is not one of float, double, or long double. |
| Member type | Definition |
|---|---|
result_type (C++11) | RealType |
param_type (C++11) | the type of the parameter set, see RandomNumberDistribution. |
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(C++11) | constructs new distribution (public member function) |
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(C++11) | resets the internal state of the distribution (public member function) |
Generation |
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(C++11) | generates the next random number in the distribution (public member function) |
Characteristics |
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(C++11) | returns the distribution parameters (public member function) |
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(C++11) | gets or sets the distribution parameter object (public member function) |
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(C++11) | returns the minimum potentially generated value (public member function) |
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(C++11) | returns the maximum potentially generated value (public member function) |
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(C++11)(C++11)(removed in C++20) | compares two distribution objects (function) |
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(C++11) | performs stream input and output on pseudo-random number distribution (function template) |
#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
| Weisstein, Eric W. "Log Normal Distribution." From MathWorld — A Wolfram Web Resource. |
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