std::exponential_distribution
From cppreference.com
Defined in header <random>
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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
Contents |
[edit] Member types
Member type | Definition |
result_type | RealType |
param_type | the type of the parameter set, unspecified |
[edit] Member functions
constructs new distribution (public member function) | |
resets the internal state of the distribution (public member function) | |
Generation | |
generates the next random number in the distribution (public member function) | |
Characteristics | |
returns the lambda distribution parameter (rate of events) (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) |
[edit] Non-member functions
compares two distribution objects (function) | |
performs stream input and output on pseudo-random number distribution (function) |
[edit] Example
#include <iostream> #include <iomanip> #include <string> #include <map> #include <random> 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 p : hist) { std::cout << std::fixed << std::setprecision(1) << p.first/2.0 << '-' << (p.first+1)/2.0 << ' ' << std::string(p.second/200, '*') << '\n'; }
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.