function cdf = birthday_cdf ( n )
%*****************************************************************************80
%
%% BIRTHDAY_CDF returns the Birthday Concurrence CDF.
%
% Licensing:
%
% This code is distributed under the GNU LGPL license.
%
% Modified:
%
% 26 August 2006
%
% Author:
%
% John Burkardt
%
% Parameters:
%
% Input, integer N, the number of people whose birthdays have been
% disclosed.
%
% Output, real CDF, the probability that at least
% two of the N people have matching birthays.
%
if ( n < 1 )
cdf = 0.0;
return
elseif ( 365 < n )
cdf = 1.0;
return
end
%
% Compute the probability that N people have distinct birthdays.
%
cdf = 1.0;
for i = 1 : n
cdf = cdf * ( 365 + 1 - i ) / 365.0;
end
%
% Compute the probability that it is NOT the case that N people
% have distinct birthdays. This is the cumulative probability
% that person 2 matches person 1, or person 3 matches 1 or 2,
% etc.
%
cdf = 1.0 - cdf;
return
end