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

function [classify, err] = classification_error(D, patterns, targets, region) 
 
%Find a classification error for a given decision surface D and a given set of 
%patterns (2xL) and targets (1xL) 
%The patterns are assumed to lay in a box defined by region 
%([-x x -y y ... number_of_points]) 
 
 
N		= region(length(region));			%Number of points on the grid 
N0		= length(find(targets == 0));		%Number of targets from class 0 
N1		= length(find(targets == 1));		%Number of targets from class 1 
Dims	= size(patterns,1);					%Number of data dimentions 
ok0	= 0; 
ok1	= 0; 
 
%Normalize the patterns according to the grid, and then check each point if it is 
%classified correctly or not. 
for i = 1:Dims, 
   base = (i-1)*2; 
	patterns(i,:) = round(1/(region(base+2)-region(base+1))*... 
      ((N-1)*patterns(i,:)+region(base+2)-N*region(base+1))); 
end 
 
switch Dims, 
case 2, 
   for i = 1:N0+N1, 
      %Get the pattern, but if for some reason it is out of range, put it on the edge of the range 
      pattern1 = min(max(1,patterns(1,i)),region(5)); 
      pattern2 = min(max(1,patterns(2,i)),region(5)); 
   	if (targets(i)), 
      	ok1		 = ok1 + (D(pattern2,pattern1) == 1); 
	   else     
   	   ok0		 = ok0 + (D(pattern2,pattern1) == 0); 
      end  
   end 
case 3, 
   for i = 1:N0+N1, 
      pattern1 = min(max(1,patterns(1,i)),region(5)); 
      pattern2 = min(max(1,patterns(2,i)),region(5)); 
      pattern3 = min(max(1,patterns(3,i)),region(5)); 
   	if (targets(i)), 
      	ok1		 = ok1 + (D(pattern2,pattern1,pattern3) == 1); 
	   else     
   	   ok0		 = ok0 + (D(pattern2,pattern1,pattern3) == 0); 
      end  
   end 
otherwise 
   error('The toolbox can assess the error for two or three dimensional data only.') 
end 
 
 
classify 		= zeros(2); 
if (N0 > 0), 
    classify(1,1)  = ok0/N0; 
    classify(1,2)  = (N0-ok0)/N0; 
end 
if (N1 > 0), 
    classify(2,2)  = ok1/N1; 
    classify(2,1)  = (N1-ok1)/N1; 
end 
 
err = (N0*classify(1,2) + N1*classify(2,1))/(N0+N1);