%GENCLASS Generate class frequency distribution
%
% M = GENCLASS(N,P)
%
% INPUT
% N Number (scalar)
% P Prior probabilities
%
% OUTPUT
% M Class frequency distribution
%
% DESCRIPTION
% Generates a class frequency distribution M of N (scalar) samples
% over a set of classes with prior probabilities given by the vector P.
% The numbers of elements in P determines the number of classes and
% thereby the number of elements in M. P should be such that SUM(P) = 1.
% If N is a vector with length C, then M=N is returned. This transparent
% behavior is implemented to avoid tests in other routines.
%
% Note that this is a random process, so M = GENCLASS(100,[0.5, 0.5])
% may result in M = [45 55].
%
% This routines is used in various data generation routines like
% GENDATH to determine the distribution of the objects over the classes.
% Copyright: R.P.W. Duin, duin@ph.tn.tudelft.nl
% Faculty of Applied Sciences, Delft University of Technology
% P.O. Box 5046, 2600 GA Delft, The Netherlands
% $Id: genclass.m,v 1.3 2006/09/26 12:55:32 duin Exp $
function N = genclass(N,p)
if nargin < 2 | isempty(p)
p = ones(1,length(N))/length(N);
end
c = length(p);
if length(N) == c
;
elseif length(N) > 1
error('Mismatch in numbers of classes')
else
if nargin < 2 | isempty(p)
p = repmat(1/c,1,c);
end
P = cumsum(p(:)');
if abs(P(c)-1) > 1e-10
error('Sum of class prior probabilities should be one')
end
X = rand(N,1);
P = [0 P];
Z = zeros(1,c);
for j=1:c
Z(j) = sum((X > P(j)) & (X <= P(j+1)));
end
N = Z;
% K = repmat(X,1,c) < repmat(P(:)',N,1);
% L = sum(K,1);
% N = L - [0 L(1:c-1)];
end
return