Random

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CGAL::Random

Definition

The class Random is a random numbers generator. It generates uniformly distributed random bools, ints and doubles. It can be used as the random number generating function object in the STL algorithm random_shuffle.

Instances of Random can be seen as input streams. Different streams are independent of each other, i.e. the sequence of numbers from one stream does not depend upon how many numbers were extracted from the other streams. At each time, an instance has a state that uniquely determines the subsequent numbers being produced.

It can be very useful, e.g. for debugging, to reproduce a sequence of random numbers. This can be done by either initialising with a fixed seed, or by using the state functions as described below.

#include <CGAL/Random.h>

Types

Random::State
	The State type.

Creation

Random random;
	introduces a variable random of type Random. The seed is chosen ``randomly'', depending on the system time.

Random random ( unsigned int seed);
	introduces a variable random of type Random and initializes its internal state using seed. Equal values for seed result in equal sequences of random numbers.

Operations

bool	random.get_bool ()	returns a random bool.

template <int b>
int	random.get_bits ()	returns a random int value from the interval [0,2^b). This is supposed to be efficient.

int	random.get_int ( int lower, int upper)
		returns a random int from the interval [lower,upper).

double	random.get_double ( double lower = 0.0, double upper = 1.0)
		returns a random double from the interval [lower,upper).

Distributions

The following member functions are a 1-to-1 correspondence to some distributions from the boost random library.

template <typename IntType>
IntType	random.uniform_smallint ( IntType lower=0, IntType upper=9)
		returns a random IntType from the interval [lower,upper]. IntType can be an integral type as int, std::ptrdiff_t, std::size_t,etc. *Warning: In contrast to get_int* this function may return upper.**

template <typename IntType>
IntType	random.uniform_int ( IntType lower=0, IntType upper=9)
		returns a random IntType from the interval [lower,upper]. IntType can be an integral type as int, std::ptrdiff_t, std::size_t,etc. *Warning: In contrast to get_int* this function may return upper.**

template <typename RealType>
Realtype	random.uniform_real ( RealType lower = 0.0, RealType upper = 1.0)
		returns a random RealType from the interval [lower,upper). RealType can be float, double, etc.

template <typename RealType>
RealType	random.uniform_01 ()	returns a random RealType from the interval [0,1). RealType can be float, double, etc.

template <typename IntType>
IntType	random ( IntType upper )	returns randomuniform_int<IntType>( 0, upper-1).

Seed and State Functions

unsigned int	random.get_seed () const	returns the seed used for initialization.

void	random.save_state ( State& state) const
		saves the current internal state in state.

void	random.restore_state ( State state)
		restores the internal state from state.

Equality Test

bool

random == random2 const

returns true, iff random and random2 have equal internal states.

Implementation

We use the boost random library function boost::rand48 to generate the random numbers.