A class for sampling random values from a given probability distribution using the alias table technique. More...

#include <egs_alias_table.h>

Public Member Functions
	EGS_AliasTable ()
	Construct an empty (uninitialized) alias table. More...

	EGS_AliasTable (const EGS_AliasTable &t)
	Copy constructor. Performs a deep copy.

	EGS_AliasTable (int N, const EGS_Float x, const EGS_Float f, int Type=1)
	Construct an alias table from the tabulated distribution with N bins with probabilities f at the bins x. More...

	EGS_AliasTable (EGS_Float xmin, EGS_Float xmax, EGS_Float accu, int nmax, EGS_AtFunction func, void *data)
	Construct an alias table for sampling values in the interval xmin ... xmax for the function func. More...

void	initialize (int N, const EGS_Float x, const EGS_Float f, int Type=1)
	Initialize the alias table. More...

int	initialize (EGS_Float xmin, EGS_Float xmax, EGS_Float accu, int nmax, EGS_AtFunction func, void *data)
	Initialize the alias table. More...

EGS_Float	sample (EGS_RandomGenerator *rndm) const
	Get a random point from this table using the RNG rndm.

int	sampleBin (EGS_RandomGenerator *rndm) const
	Get a random bin from this table.

EGS_Float	getAverage () const
	Get the average of the probability distribution represented by this alias table object.

EGS_Float	getMaximum () const
	Get the maximum abscissa of this alias table object.

Detailed Description

A class for sampling random values from a given probability distribution using the alias table technique.

Instances of this class can be used to efficiently sample random variables from any probability distribution. The probability distribution is represented internally as an alias table. EGS_AliasTable objects can be initialized from a distribution tabulated as discrete values, as a histogram, or as function values at bin edges and a linear interpolation between these values (see this constructor ), or from a function within a specified interval (see this constructor ) Random values are then drawn using the sample() method.

Definition at line 63 of file egs_alias_table.h.

Constructor & Destructor Documentation

EGS_AliasTable::EGS_AliasTable ( )

Construct an empty (uninitialized) alias table.

The table should be initialized using one of the initialize() methods before using it for sampling.

Definition at line 72 of file egs_alias_table.h.

EGS_AliasTable::EGS_AliasTable	(	int	N,
		const EGS_Float *	x,
		const EGS_Float *	f,
		int	Type = `1`
	)

Construct an alias table from the tabulated distribution with N bins with probabilities f at the bins x.

If Type = 0, the N x values are interpreted as discrete abscissas, i.e. the probability distribution is assumend to be $\sum f_i \delta(x - x_i)$ , where $\delta$ is Dirac's delta function. If Type is 1, the distribution is assumed to be a histogram with N-1 bins with the $i$ 'th bin between $x_i$ and $x_{i+1}$ having a probability $f_i$ . If Type is 2, the distribution is assumed to be continuous with a linear variation between the $x_i,f_i$ and $x_{i+1},f_{i+1}$ .

Definition at line 93 of file egs_alias_table.h.

EGS_AliasTable::EGS_AliasTable	(	EGS_Float	xmin,
		EGS_Float	xmax,
		EGS_Float	accu,
		int	nmax,
		EGS_AtFunction	func,
		void *	data
	)

Construct an alias table for sampling values in the interval xmin ... xmax for the function func.

The interval xmin ... xmax is divided into interpolation intervals in such a way that the error using a linear interpolation does not exceed accu. However, if the number of bins needed to achieve an interpolation accuracy of accu is larger than nmax, no more than nmax bins are used. Internally the alias table will be set to be of type 2.

Definition at line 109 of file egs_alias_table.h.

Member Function Documentation

void EGS_AliasTable::initialize	(	int	N,
		const EGS_Float *	x,
		const EGS_Float *	f,
		int	Type = `1`
	)

Initialize the alias table.

See the constructor with corresponding arguments.

Definition at line 100 of file egs_alias_table.cpp.

int EGS_AliasTable::initialize	(	EGS_Float	xmin,
		EGS_Float	xmax,
		EGS_Float	accu,
		int	nmax,
		EGS_AtFunction	func,
		void *	data
	)

Initialize the alias table.

See the constructor with corresponding arguments. Return value is 0 on success (the accuracy goal was satisfied with less than nmax bins), 1 if it was not possible to get the required interpolation accuracy with nmax bins.

Definition at line 195 of file egs_alias_table.cpp.

References egsFatal, and loopMax.

The documentation for this class was generated from the following files:

/home/rwtownson/EGSnrc/HEN_HOUSE/egs++/egs_alias_table.h
/home/rwtownson/EGSnrc/HEN_HOUSE/egs++/egs_alias_table.cpp

Public Member Functions

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation