aib.h File Reference

AIB (Agglomerative Information Bottleneck (AIB)) More...

#include "generic.h"
#include "mathop.h"

Data Structures
struct	VlAIB
	AIB algorithm data. More...

Functions
void	vl_aib_set_verbosity (VlAIB *self, int verbosity)
	Set the verbosity.
int	vl_aib_get_verbosity (VlAIB const *self)
	Get the verbosity.
Create and destroy
VlAIB *	vl_aib_new (double *Pcx, vl_uint nvalues, vl_uint nlabels)
	Allocates and initializes the internal data structure.
void	vl_aib_delete (VlAIB *aib)
	Deletes AIB data structure.
Process data
void	vl_aib_process (VlAIB *aib)
	Runs AIB on Pcx.
Retrieve results
vl_uint *	vl_aib_get_parents (VlAIB const *aib)
	Get resulting list of parents.
double *	vl_aib_get_costs (VlAIB const *aib)
	Get a list of merge costs.

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Detailed Description

Author:

Brian Fulkerson

Andrea Vedaldi

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Function Documentation

void vl_aib_delete

(

VlAIB *

aib

)

Parameters:

aib	data structure to delete.

double * vl_aib_get_costs ( VlAIB const *  aib )

inline

Parameters:

aib	AIB filter.

Returns:

An array of costs

vl_uint * vl_aib_get_parents ( VlAIB const *  aib )

inline

Parameters:

aib	AIB filter.

Returns:

An array of parents

int vl_aib_get_verbosity ( VlAIB const *  self )

inline

Parameters:

self	AIB object.

Returns:

the verbosity level.

VlAIB* vl_aib_new	(	double *	Pcx,
		vl_uint	nvalues,
		vl_uint	nlabels
	)

Parameters:

Pcx	A pointer to a 2D array of probabilities
nvalues	The number of rows in the array
nlabels	The number of columns in the array

Creates a new VlAIB struct containing pointers to all the data that will be used during the AIB process.

Allocates memory for the following:

• Px (nvalues*sizeof(double))
• Pc (nlabels*sizeof(double))
• nodelist (nvalues*sizeof(vl_uint))
• which (nvalues*sizeof(vl_uint))
• beta (nvalues*sizeof(double))
• bidx (nvalues*sizeof(vl_uint))
• parents ((2*nvalues-1)*sizeof(vl_uint))
• costs (nvalues*sizeof(double))

Since it simply copies to pointer to Pcx, the total additional memory requirement is:

(3*nvalues+nlabels)*sizeof(double) + 4*nvalues*sizeof(vl_uint)

Returns:

An allocated and initialized VlAIB pointer

void vl_aib_process

(

VlAIB *

aib

)

Parameters:

aib	AIB object to process

The function runs Agglomerative Information Bottleneck (AIB) on the joint probability table aib->Pcx which has labels along the columns and feature values along the rows. AIB iteratively merges the two values of the feature x that causes the smallest decrease in mutual information between the random variables x and c.

Merge operations are arranged in a binary tree. The nodes of the tree correspond to the original feature values and any other value obtained as a result of a merge operation. The nodes are indexed in breadth-first order, starting from the leaves. The first index is zero. In this way, the leaves correspond directly to the original feature values. In total there are 2*nvalues-1 nodes.

The results may be accessed through vl_aib_get_parents which returns an array with one element per tree node. Each element is the index the parent node. The root parent is equal to zero. The array has 2*nvalues-1 elements.

Feature values with null probability are ignored by the algorithm and their nodes have parents indexing a non-existent tree node (a value bigger than 2*nvalues-1).

Then the function will also compute the information level after each merge. vl_get_costs will return a vector with the information level after each merge. cost has nvalues entries: The first is the value of the cost functional before any merge, and the others are the cost after the nvalues-1 merges.

void vl_aib_set_verbosity ( VlAIB *  self, int  verbosity  )

inline

Parameters:

self	AIB object.
verbosity	a non-negative integer.