function f = exp_pdf(X,muX)
% f = exp_pdf(X,muX)
% return PDF of exponential distribution with mean muX, at points X
%
%    Reference: http://en.wikipedia.org/wiki/Exponential_distribution

  idx = find(X<0);
  X(idx) = 0.01;

  f =  exp(-X/muX) / muX;

% ----------------------------------------------------------------- exp_pdf
