std::exponential_distribution
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exponential_distribution
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std::exponential_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 exponential_distribution;
(since C++11)
class exponential_distribution;
Produces random non-negative floating-point values \(\small x\)x, distributed according to probability density function:
- \(\small P(x|\lambda) = \lambda e^{-\lambda x}\)P(x|λ) = λe-λx
The value obtained is the time/distance until the next random event if random events occur at constant rate \(\small\lambda\)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 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] 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 (auto const& [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.