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# geometric_distribution Class

Visual Studio 2015

The latest version of this topic can be found at geometric_distribution Class.

Generates a geometric distribution.

## Syntax

```class geometric_distribution {
public:
// types
typedef IntType result_type;
struct param_type;
// constructors and reset functions
explicit geometric_distribution(double p = 0.5);
explicit geometric_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 double p() const;
param_type param() const;
void param(const param_type& parm);
result_type min() const;
result_type max() const;
};

```

#### Parameters

`IntType`
The integer result type, defaults to `int`. For possible types, see <random>.

## Remarks

The template class describes a distribution that produces values of a user-specified integral type with a geometric distribution. The following table links to articles about individual members.

geometric_distribution::geometric_distribution`geometric_distribution::p``geometric_distribution::param`
`geometric_distribution::operator()`geometric_distribution::param_type

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

For detailed information about the chi-squared distribution, see the Wolfram MathWorld article Geometric Distribution.

## Example

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

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

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

std::geometric_distribution<> distr(p);

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

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

// print results
std::cout << "Distribution for " << s << " samples:" << std::endl;
for (const auto& elem : histogram) {
std::cout << std::setw(5) << elem.first << ' ' << std::string(elem.second, ':') << std::endl;
}
std::cout << std::endl;
}

int main()
{
double p_dist = 0.5;

int samples = 100;

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 \'p\' distribution parameter: ";
std::cin >> p_dist;
std::cout << "Enter an integer value for the sample count: ";
std::cin >> samples;

test(p_dist, samples);
}

```

## Output

First test:

```Use CTRL-Z to bypass data entry and run using default values.Enter a floating point value for the 'p' distribution parameter: .5Enter an integer value for the sample count: 100min() == 0max() == 2147483647p() == 0.5000000000Distribution for 100 samples:    0 ::::::::::::::::::::::::::::::::::::::::::::::::::::    1 ::::::::::::::::::::::::    2 ::::::::::::::    3 :::::    4 ::    5 ::    6 :

```

Second test:

```Use CTRL-Z to bypass data entry and run using default values.Enter a floating point value for the 'p' distribution parameter: .1Enter an integer value for the sample count: 100min() == 0max() == 2147483647p() == 0.1000000000Distribution for 100 samples:    0 :::::::::    1 :::::::::::    2 :::::::    3 ::::::::    4 ::::::::    5 ::::::    6 :::::    7 ::::::    8 :::::    9 ::::   10 ::::   11 ::   12 :   13 :   14 :::   15 ::::   16 :::   17 :   18 :   19 :   20 ::   21 :   22 :   23 :   28 ::   33 :   35 :   40 :

```

Namespace: std

## geometric_distribution::geometric_distribution

Constructs the distribution.

```explicit geometric_distribution(RealType p = 0.5);

explicit geometric_distribution(const param_type& parm);

```

### Parameters

`p`
The `p` distribution parameter.

`parm`
The parameter structure used to construct the distribution.

### Remarks

Precondition: `0.0 < p && p < 1.0`

The first constructor constructs an object whose stored `p` value holds the value `p`.

The second constructor constructs an object whose stored parameters are initialized from `parm`. You can obtain and set the current parameters of an existing distribution by calling the `param()` member function.

## geometric_distribution::param_type

Stores the parameters of the distribution.

struct param_type {
typedef geometric_distribution<IntType, RealType> distribution_type;
param_type(RealType p = 0.5); RealType p() const; .....
bool operator==(const param_type& right) const; bool operator!=(const param_type& right) const; };

### Parameters

See parent topic geometric_distribution Class.

### Remarks

Precondition: `0.0 < p && p < 1.0`

This structure can be passed to the distribution's class constructor at instantiation, to the `param()` member function to set the stored parameters of an existing distribution, and to `operator()` to be used in place of the stored parameters.