TMVA::CostComplexityPruneTool Class Reference

A class to prune a decision tree using the Cost Complexity method.

(see "Classification and Regression Trees" by Leo Breiman et al)

Some definitions:

• \( T_{max} \) - the initial, usually highly overtrained tree, that is to be pruned back
• \( R(T) \) - quality index (Gini, misclassification rate, or other) of a tree \( T \)
• \( \sim T \) - set of terminal nodes in \( T \)
• \( T' \) - the pruned subtree of \( T_max \) that has the best quality index \( R(T') \)
• \( \alpha \) - the prune strength parameter in Cost Complexity pruning \( (R_{\alpha}(T) = R(T) + \alpha*|\sim T|) \)

There are two running modes in CCPruner: (i) one may select a prune strength and prune back the tree \( T_{max}\) until the criterion:

\[ \alpha < \frac{R(T) - R(t)}{|\sim T_t| - 1} \]

is true for all nodes t in \( T \), or (ii) the algorithm finds the sequence of critical points \( \alpha_k < \alpha_{k+1} ... < \alpha_K \) such that \( T_K = root(T_{max}) \) and then selects the optimally-pruned subtree, defined to be the subtree with the best quality index for the validation sample.

Definition at line 62 of file CostComplexityPruneTool.h.

Public Member Functions
	CostComplexityPruneTool (SeparationBase *qualityIndex=nullptr)
	the constructor for the cost complexity pruning
virtual	~CostComplexityPruneTool ()
	the destructor for the cost complexity pruning
virtual PruningInfo *	CalculatePruningInfo (DecisionTree *dt, const IPruneTool::EventSample *testEvents=nullptr, Bool_t isAutomatic=kFALSE)
	the routine that basically "steers" the pruning process.
Public Member Functions inherited from TMVA::IPruneTool
	IPruneTool ()
virtual	~IPruneTool ()
Double_t	GetPruneStrength () const
Bool_t	IsAutomatic () const
void	SetAutomatic ()
void	SetPruneStrength (Double_t alpha)

Private Member Functions
void	InitTreePruningMetaData (DecisionTreeNode *n)
	initialise "meta data" for the pruning, like the "costcomplexity", the critical alpha, the minimal alpha down the tree, etc... for each node!!
MsgLogger &	Log () const
	output stream to save logging information
void	Optimize (DecisionTree *dt, Double_t weights)
	after the critical \( \alpha \) values (at which the corresponding nodes would be pruned away) had been established in the "InitMetaData" we need now: automatic pruning:

Private Attributes
MsgLogger *	fLogger
Int_t	fOptimalK
	! the optimal index of the prune sequence
std::vector< DecisionTreeNode * >	fPruneSequence
	! map of weakest links (i.e., branches to prune) -> pruning index
std::vector< Double_t >	fPruneStrengthList
	! map of alpha -> pruning index
std::vector< Double_t >	fQualityIndexList
	! map of R(T) -> pruning index
SeparationBase *	fQualityIndexTool
	! the quality index used to calculate R(t), R(T) = sum[t in ~T]{ R(t) }

Additional Inherited Members
Public Types inherited from TMVA::IPruneTool
typedef std::vector< const Event * >	EventSample
Protected Attributes inherited from TMVA::IPruneTool
Double_t	B
Double_t	fPruneStrength
	! regularization parameter in pruning
Double_t	S

#include <TMVA/CostComplexityPruneTool.h>

Inheritance diagram for TMVA::CostComplexityPruneTool:

Constructor & Destructor Documentation

CostComplexityPruneTool()

CostComplexityPruneTool::CostComplexityPruneTool

(

SeparationBase *

qualityIndex = nullptr

)

the constructor for the cost complexity pruning

Definition at line 68 of file CostComplexityPruneTool.cxx.

~CostComplexityPruneTool()

CostComplexityPruneTool::~CostComplexityPruneTool ( )

virtual

the destructor for the cost complexity pruning

Definition at line 89 of file CostComplexityPruneTool.cxx.

Member Function Documentation

CalculatePruningInfo()

PruningInfo * CostComplexityPruneTool::CalculatePruningInfo ( DecisionTree * dt, const IPruneTool::EventSample * validationSample = nullptr, Bool_t isAutomatic = kFALSE )

virtual

the routine that basically "steers" the pruning process.

Call the calculation of the pruning sequence, the tree quality and alike..

Implements TMVA::IPruneTool.

Definition at line 98 of file CostComplexityPruneTool.cxx.

InitTreePruningMetaData()

void CostComplexityPruneTool::InitTreePruningMetaData ( DecisionTreeNode * n )

private

initialise "meta data" for the pruning, like the "costcomplexity", the critical alpha, the minimal alpha down the tree, etc... for each node!!

Definition at line 181 of file CostComplexityPruneTool.cxx.

Log()

MsgLogger & TMVA::CostComplexityPruneTool::Log ( ) const

inlineprivate

output stream to save logging information

Definition at line 87 of file CostComplexityPruneTool.h.

Optimize()

void CostComplexityPruneTool::Optimize ( DecisionTree * dt, Double_t weights )

private

after the critical \( \alpha \) values (at which the corresponding nodes would be pruned away) had been established in the "InitMetaData" we need now: automatic pruning:

find the value of \( \alpha \) for which the test sample gives minimal error, on the tree with all nodes pruned that have \( \alpha_{critical} < \alpha \), fixed parameter pruning

Definition at line 236 of file CostComplexityPruneTool.cxx.

Member Data Documentation

fLogger

MsgLogger* TMVA::CostComplexityPruneTool::fLogger

mutableprivate

Definition at line 86 of file CostComplexityPruneTool.h.

fOptimalK

Int_t TMVA::CostComplexityPruneTool::fOptimalK

private

! the optimal index of the prune sequence

Definition at line 77 of file CostComplexityPruneTool.h.

fPruneSequence

std::vector<DecisionTreeNode*> TMVA::CostComplexityPruneTool::fPruneSequence

private

! map of weakest links (i.e., branches to prune) -> pruning index

Definition at line 73 of file CostComplexityPruneTool.h.

fPruneStrengthList

std::vector<Double_t> TMVA::CostComplexityPruneTool::fPruneStrengthList

private

! map of alpha -> pruning index

Definition at line 74 of file CostComplexityPruneTool.h.

fQualityIndexList

std::vector<Double_t> TMVA::CostComplexityPruneTool::fQualityIndexList

private

! map of R(T) -> pruning index

Definition at line 75 of file CostComplexityPruneTool.h.

fQualityIndexTool

SeparationBase* TMVA::CostComplexityPruneTool::fQualityIndexTool

private

! the quality index used to calculate R(t), R(T) = sum[t in ~T]{ R(t) }

Definition at line 71 of file CostComplexityPruneTool.h.

Libraries for TMVA::CostComplexityPruneTool:

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

• tmva/tmva/inc/TMVA/CostComplexityPruneTool.h
• tmva/tmva/src/CostComplexityPruneTool.cxx