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matlab/rtsROC.m 889 Bytes
1ff9af85   David Mayerich   added MATLAB/OCTA...
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  function [ROC, AUC, T] = rtsROC(thresholds, class)
  
  %Computes the ROC curves given a set of thresholds and class assignments
  % class = boolean array describing actual class membership
  % thresholds = threshold values for class assignment
  % ROC = ROC curve as column vectors (1 = 1-specificity, 2 = sensitivity)
  % AUC = area under the ROC curve computed using the trapezoid method
  % T = threshold values associated with each 1-specificity value
  
  nValues = length(thresholds);
  ROC = zeros(nValues, 2);
  
  %sort both arrays
  [T, ix] = sort(thresholds, 'descend');
  C = class(ix);
  
  %compute the necessary global values
  P = nnz(class);
  N = nValues - P;
  
  for i = 1:nValues
      TP = nnz(C(1:i));
      sensitivity = TP/P;
      
      FP = i - TP;
      FPR = FP/N;
      specificity = 1 - FPR;
      
      ROC(i, 1) = 1 - specificity;
      ROC(i, 2) = sensitivity;
  end
  
  AUC = trapz(ROC(:, 1), ROC(:, 2));