function [pd, pf, err] = roc(cnt,prob1,prob2)
% roc: function which returns the receiver-operating characteristics and
% the error rate characterizing the ability of an ideal observer to
% discriminate between the two distributions.
%
%	[pd, pf, err] = roc(cnt,prob1,prob2)
%
%	where 
%	  cnt = vector of spike counts for both distributions
%	  prob1 = first (null) probability distribution of counts
%	  prob2 = second probability distribution of counts
%
% The return parameters are:
%	pd = probability of correct detection
%	pf = probability of false-alarm
%       err = error rate
%  


if ( nargin ~= 3 )
  disp(' ');
  disp('usage: roc(cnt,prob1,prob2) ');
  disp('       for more information type "help roc" in the main');
  disp('       matlab window');
  disp(' ');
  return;
end;

%initializes the various variables
prob1 = prob1(:);
prob2 = prob2(:);
n_cnt = length(cnt);
pd = zeros(n_cnt+2,1);
pf = zeros(n_cnt+2,1);
err = zeros(n_cnt+2,1);

for k = 1:n_cnt
  pf(k+1,1) = sum(prob1(k:n_cnt,1));
  pd(k+1,1) = sum(prob2(k:n_cnt,1));
end;

pf(1,1) = 1;
pd(1,1) = 1;

err = 0.5*(pf + 1 - pd);