www.pudn.com > Classification_toolbox.part01.rar > CARTfunctions.m

function delta = CARTfunctions(split_point, patterns, targets, dim, split_type) 
 
%Calculate the difference in impurity for the CART algorithm 
Uc	= unique(targets); 
for i = 1:length(Uc), 
   in		= find(targets == Uc(i)); 
   Pr(i)	= length(find(patterns(dim, in) >   split_point))/length(in); 
   Pl(i)	= length(find(patterns(dim, in) <=  split_point))/length(in); 
end 
 
switch split_type, 
case 'Entropy' 
	Er		= sum(-Pr.*log(Pr+eps)/log(2)); 
   El		= sum(-Pl.*log(Pl+eps)/log(2)); 
case {'Variance', 'Gini'} 
	Er		= 1 - sum(Pr.^2); 
   El		= 1 - sum(Pl.^2); 
case 'Missclassification' 
   Er		= 1 - max(Pr); 
   El		= 1 - max(Pl); 
otherwise 
   error('Possible splitting rules are: Entropy, Variance, Gini, or Missclassification') 
end 
 
P		= length(find(patterns(dim, :) <= split_point)) / length(targets); 
delta = -P*El - (1-P)*Er;