# 28 Numerics library [numerics]

## 28.5 Random number generation [rand]

### 28.5.9 Random number distribution class templates [rand.dist]

#### 28.5.9.4.2 Class template exponential_distribution[rand.dist.pois.exp]

An exponential_distribution random number distribution produces random numbers distributed according to the probability density function
namespace std { template<class RealType = double> class exponential_distribution { public: // types using result_type = RealType; using param_type = unspecified; // constructors and reset functions exponential_distribution() : exponential_distribution(1.0) {} explicit exponential_distribution(RealType lambda); explicit exponential_distribution(const param_type& parm); void reset(); // equality operators friend bool operator==(const exponential_distribution& x, const exponential_distribution& y); // generating functions template<class URBG> result_type operator()(URBG& g); template<class URBG> result_type operator()(URBG& g, const param_type& parm); // property functions RealType lambda() const; param_type param() const; void param(const param_type& parm); result_type min() const; result_type max() const; // inserters and extractors template<class charT, class traits> friend basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& os, const exponential_distribution& x); template<class charT, class traits> friend basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>& is, exponential_distribution& x); }; }
```explicit exponential_distribution(RealType lambda); ```
Preconditions: .
Remarks: lambda corresponds to the parameter of the distribution.
```RealType lambda() const; ```
Returns: The value of the lambda parameter with which the object was constructed.