std::exponential_distribution
From cppreference.com
Defined in header <random> | ||
template<class RealType =double> class exponential_distribution; | (since C++11) | |
Produces random non-negative floating-point values x, distributed according to probability density function:
- P(x|λ) = λe-λx
The value obtained is the time/distance until the next random event if random events occur at constant rate λ per unit of time/distance. For example, this distribution describes the time between the clicks of a Geiger counter or the distance between point mutations in a DNA strand.
This is the continuous counterpart of std::geometric_distribution.
std::exponential_distribution satisfies 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 longdouble. |
[edit]Member types
| Member type | Definition |
result_type(C++11) | RealType |
param_type(C++11) | the type of the parameter set, see RandomNumberDistribution. |
[edit]Member functions
(C++11) | constructs new distribution (public member function) |
(C++11) | resets the internal state of the distribution (public member function) |
Generation | |
(C++11) | generates the next random number in the distribution (public member function) |
Characteristics | |
(C++11) | returns the lambda distribution parameter (rate of events) (public member function) |
(C++11) | gets or sets the distribution parameter object (public member function) |
(C++11) | returns the minimum potentially generated value (public member function) |
(C++11) | returns the maximum potentially generated value (public member function) |
[edit]Non-member functions
(C++11)(C++11)(removed in C++20) | compares two distribution objects (function) |
(C++11) | performs stream input and output on pseudo-random number distribution (function template) |
[edit]Notes
Some implementations may occasionally return infinity if RealType is float. This is LWG issue 2524.
[edit]Example
Run this code
#include <iomanip>#include <iostream>#include <map>#include <random>#include <string> int main(){std::random_device rd;std::mt19937 gen(rd()); // if particles decay once per second on average,// how much time, in seconds, until the next one? std::exponential_distribution<> d(1); std::map<int, int> hist;for(int n =0; n !=10000;++n)++hist[2* d(gen)]; for(autoconst&[x, y]: hist)std::cout<<std::fixed<<std::setprecision(1)<< x /2.0<<'-'<<(x +1)/2.0<<' '<<std::string(y /200, '*')<<'\n';}
Possible output:
0.0-0.5 ******************* 0.5-1.0 *********** 1.0-1.5 ******* 1.5-2.0 **** 2.0-2.5 ** 2.5-3.0 * 3.0-3.5 3.5-4.0
[edit]External links
| Weisstein, Eric W. "Exponential Distribution." From MathWorld — A Wolfram Web Resource. |
