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| Mathematical constants(C++20) | |||||||||||||||||||||||||||||||
| Basic linear algebra algorithms(C++26) | |||||||||||||||||||||||||||||||
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| Floating-point environment(C++11) | |||||||||||||||||||||||||||||||
| Complex numbers | |||||||||||||||||||||||||||||||
Numeric array (valarray) | |||||||||||||||||||||||||||||||
| Pseudo-random number generation | |||||||||||||||||||||||||||||||
| Bit manipulation(C++20) | |||||||||||||||||||||||||||||||
| Saturation arithmetic(C++26) | |||||||||||||||||||||||||||||||
| Factor operations | |||||||||||||||||||||||||||||||
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| Interpolations | |||||||||||||||||||||||||||||||
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| Generic numeric operations | |||||||||||||||||||||||||||||||
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| C-style checked integer arithmetic | |||||||||||||||||||||||||||||||
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| 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) | |
Produces random non-negative floating-point values\(\small x\)x, distributed according to probability density function:
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 ofstd::geometric_distribution.
std::exponential_distribution satisfiesRandomNumberDistribution.
Contents |
| RealType | - | The result type generated by the generator. The effect is undefined if this is not one offloat,double, orlongdouble. |
| Member type | Definition |
result_type(C++11) | RealType |
param_type(C++11) | the type of the parameter set, seeRandomNumberDistribution. |
(C++11) | constructs new distribution (public member function)[edit] |
(C++11) | resets the internal state of the distribution (public member function)[edit] |
Generation | |
(C++11) | generates the next random number in the distribution (public member function)[edit] |
Characteristics | |
(C++11) | returns thelambda distribution parameter (rate of events) (public member function)[edit] |
(C++11) | gets or sets the distribution parameter object (public member function)[edit] |
(C++11) | returns the minimum potentially generated value (public member function)[edit] |
(C++11) | returns the maximum potentially generated value (public member function)[edit] |
(C++11)(C++11)(removed in C++20) | compares two distribution objects (function)[edit] |
(C++11) | performs stream input and output on pseudo-random number distribution (function template)[edit] |
Some implementations may occasionally return infinity ifRealType isfloat. This isLWG issue 2524.
#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 *3.0-3.53.5-4.0
| Weisstein, Eric W. "Exponential Distribution." From MathWorld — A Wolfram Web Resource. |
