threshold.m

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function thr = threshold(d,fracrej)
%THRESHOLD Find percentile value for dataset
%
% thr = threshold(d,frac)
%
% Find the threshold for the data d. The lowest  frac*100%  of the
% data is rejected. This method is therefore first aimed at thresholds
% for density estimates. When the highest  frac*100%  of the data
% should be rejected, you have to use:   thr = -threshold(-d,frac).
% (prctile in the statistics toolbox can also be used)

% Copyright: D. Tax, R.P.W. Duin, [e-mail]
% Faculty of Applied Physics, Delft University of Technology
% P.O. Box 5046, 2600 GA Delft, The Netherlands

[nr,dim] = size(d);
if (dim>1)
  error('threshold function is expecting a 1D array');
end
if ((fracrej<0)|(fracrej>1))
  error('fracrej in threshold should be between 0 and 1');
end
d = sort(d);
frac = round(fracrej*nr);
if (frac==0)
  thr = d(1);
else
  if (frac==nr)
    thr = d(nr);
  else
    thr = (d(frac) + d(frac+1))/2;
  end
end