exponential_distribution Class

Generates an exponential distribution.

template<class RealType = double>
class exponential_distribution
{
public:
    // types
    typedef RealType result_type;
    struct param_type;
    // constructors and reset functions
    explicit exponential_distribution(RealType lambda = 1.0);
    explicit exponential_distribution(const param_type& parm);
    void reset();
    // generating functions
    template<class URNG>
    result_type operator()(URNG& gen);
    template<class URNG>
    result_type operator()(URNG& gen, 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;
};

Parameters

• RealType
  The floating-point result type, defaults to double. For possible types, see <random>.

Remarks

The template class describes a distribution that produces values of a user-specified integral type, or type double if none is provided, distributed according to the Exponential Distribution. The following table links to articles about individual members.

The property function lambda() returns the value for the stored distribution parameter lambda.

For more information about distribution classes and their members, see <random>.

For detailed information about the exponential distribution, see the Wolfram MathWorld article Exponential Distribution.

Example

// compile with: /EHsc /W4
#include <random> 
#include <iostream>
#include <iomanip>
#include <string>
#include <map>

void test(const double l, const int s) {

    // uncomment to use a non-deterministic generator
    //    std::random_device gen;
    std::mt19937 gen(1701);

    std::exponential_distribution<> distr(l);

    std::cout << std::endl;
    std::cout << "min() == " << distr.min() << std::endl;
    std::cout << "max() == " << distr.max() << std::endl;
    std::cout << "lambda() == " << std::fixed << std::setw(11) << std::setprecision(10) << distr.lambda() << std::endl;

    // generate the distribution as a histogram
    std::map<double, int> histogram;
    for (int i = 0; i < s; ++i) {
        ++histogram[distr(gen)];
    }

    // print results
    std::cout << "Distribution for " << s << " samples:" << std::endl;
    int counter = 0;
    for (const auto& elem : histogram) {
        std::cout << std::fixed << std::setw(11) << ++counter << ": "
            << std::setw(14) << std::setprecision(10) << elem.first << std::endl;
    }
    std::cout << std::endl;
}

int main()
{
    double l_dist = 0.5;
    int samples = 10;

    std::cout << "Use CTRL-Z to bypass data entry and run using default values." << std::endl;
    std::cout << "Enter a floating point value for the 'lambda' distribution parameter (must be greater than zero): ";
    std::cin >> l_dist;
    std::cout << "Enter an integer value for the sample count: ";
    std::cin >> samples;

    test(l_dist, samples);
}

Output

Use CTRL-Z to bypass data entry and run using default values.
Enter a floating point value for the 'lambda' distribution parameter (must be greater than zero): 1
Enter an integer value for the sample count: 10

min() == 0
max() == 1.79769e+308
lambda() == 1.0000000000
Distribution for 10 samples:
          1:   0.0936880533
          2:   0.1225944894
          3:   0.6443593183
          4:   0.6551171649
          5:   0.7313457551
          6:   0.7313557977
          7:   0.7590097389
          8:   1.4466885214
          9:   1.6434088411
         10:   2.1201210996

Requirements

Header: <random>

Namespace: std

See Also

Reference

<random>