std::discrete_distribution::(constructor)

(1) default constructor

The distribution will always produce zero.

(2) range constructor

The sequence of values in the range is used as the weights for each integer value from 0 to (n-1), where n is the distance between the iterators.

(3) initializer list

The sequence in the list is used as the weights for each integer value from 0 to (n-1), where n is the size of the initializer list.

(4) operation constructor

Each integer value k in the closed range between 0 and (nw-1) is given the weight resulting from calling:

fw(xmin+(xmax-xmin)*(k+0.5)/nw)

(5) param constructor

The distribution adopts the distribution parameters specified by parm.

Parameters

first, last

Input iterators to the initial and final positions in a range. The range used is [first,last), which includes all the elements between first and last, including the element pointed by first but not the element pointed by last.
If first==last, the distribution will always produce zero.
The function template type shall be an input iterator that points to some type convertible to double.

il

An initializer_list object.
These objects are automatically constructed from initializer list declarators.

nw

Number of weights: The highest possible number produced by the distribution is (nw-1).

xmin,xmax

Bounds of a range of values to be passed to fw. The first value passed to fw is (xmin+(xmax-xmin)/2*n), and then, nw values are passed with increases of ((xmax-xmin)/2).

fw

A pointer to a function or a function object that can take a single argument of a type convertible from double and return a value convertible to double.

parm

An object representing the distribution's parameters, obtained by a call to member function param.
param_type is a member type.

Example

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// discrete_distribution constructor
#include <iostream>
#include <chrono>
#include <random>
#include <functional>
#include <array>

int main()
{
  // construct a trivial random generator engine from a time-based seed:
  unsigned seed = std::chrono::system_clock::now().time_since_epoch().count();
  std::default_random_engine generator (seed);

  std::array<double,4> init = {1.0,2.0,3.0,4.0};

  std::discrete_distribution<int> first;
  std::discrete_distribution<int> second (init.begin(),init.end());
  std::discrete_distribution<int> third {0.1,0.2,0.3,0.4};
  std::discrete_distribution<int> fourth (4,0.0,40.0,std::bind2nd(std::plus<double>(),5.0));
  std::discrete_distribution<int> fifth (fourth.param());

  // display probabilities:
  std::cout << "displaying probabilities:";
  std::cout << std::endl << "first : ";
  for (double x:first.probabilities()) std::cout << x << " ";
  std::cout << std::endl << "second: ";
  for (double x:second.probabilities()) std::cout << x << " ";
  std::cout << std::endl << "third : ";
  for (double x:third.probabilities()) std::cout << x << " ";
  std::cout << std::endl << "fourth: ";
  for (double x:fourth.probabilities()) std::cout << x << " ";
  std::cout << std::endl << "fifth : ";
  for (double x:fifth.probabilities()) std::cout << x << " ";
  std::cout << std::endl;

  return 0;
}

displaying probabilities:
first : 1
second: 0.1 0.2 0.3 0.4
third : 0.1 0.2 0.3 0.4
fourth: 0.1 0.2 0.3 0.4
fifth : 0.1 0.2 0.3 0.4

Complexity

See also

discrete_distribution::reset

Reset distribution (public member function)

discrete_distribution::param

Distribution parameters (public member function)