Random

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CGAL::Random

Definition

The class Randomis 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.

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

#include <CGAL/Random.h>

Types

Random::State
	State type.

Creation

Random random;
	introduces a variable random of type Random.

Random random ( long 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.

Random random ( State state);
	introduces a variable random of type Random and initializes its internal state with state.

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).

int	random ( int upper )	returns random.get_int( 0, upper).

State Functions

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

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

Equality Test

bool

random == random2

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

Implementation

We use the C library function erand48 to generate the random numbers, i.e., the sequence of numbers depends on the implementation of erand48 on your specific platform.