function pfa=false_acc (llr, thr);
%
% Syntax: pfa=false_acc (llr, thr);
%
% Computes false acceptation  probabililty with a vector of log likelihood 
% ratios and a vector of thresholds. Assumes that the ideal decision for 
% client to be +1 and for imposter -1.
% llr is the log likelihood vector of IMPOSTERS

points=length(thr);
Nimpo=length(llr);
pfa=zeros (1,points); 
for i=1:points,
  t=thr(i);
  false_acc=length (find (llr >  t))  / Nimpo;
  pfa(i)=false_acc;
end