std::exponential_distribution - cppreference.com (original) (raw)
std::exponential_distribution
| | | | | ---------------------------------------------------------------------- | | ------------- | | template< class RealType = double > class exponential_distribution; | | (since C++11) |
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
- 1 Template parameters
- 2 Member types
- 3 Member functions
- 4 Non-member functions
- 5 Notes
- 6 Example
- 7 External links
[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 |
| param_type (C++11) | the type of the parameter set, see RandomNumberDistribution. |
[edit] Member functions
| (constructor)(C++11) | constructs new distribution (public member function) [edit] |
|---|---|
| reset(C++11) | resets the internal state of the distribution (public member function) [edit] |
| Generation | |
| operator()(C++11) | generates the next random number in the distribution (public member function) [edit] |
| Characteristics | |
| lambda(C++11) | returns the lambda distribution parameter (rate of events) (public member function) [edit] |
| param(C++11) | gets or sets the distribution parameter object (public member function) [edit] |
| min(C++11) | returns the minimum potentially generated value (public member function) [edit] |
| max(C++11) | returns the maximum potentially generated value (public member function) [edit] |
[edit] Non-member functions
[edit] Notes
Some implementations may occasionally return infinity if RealType is float. This is LWG issue 2524.
[edit] Example
#include #include #include #include #include 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