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function area = AreaUnderROC(ROC)
% area = AreaUnderROC(ROC)
%
% Compute the area under an ROC curve.
%
% xx/xx/xx dhb Wrote it.
[NFA,index] = sort(ROC(:,2));
NROC(:,1) = ROC(index,1);
NROC(:,2) = ROC(index,2);
[m,n] = size(NROC);
FROC = zeros(m+2,n);
FROC(1,:) = [0, 0];
FROC(m+2,:) = [1, 1];
FROC(2:m+1,:) = NROC;
area = 0;
totwidth = 0;
for i = 1:m+1
meanhgt = (FROC(i,1)+FROC(i+1,1))/2;
width = FROC(i+1,2)-FROC(i,2);
area = area+meanhgt*width;
totwidth = totwidth+width;
end
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