function [H] = entropy_base( P,b )
%Calculate the entropy of a single
%random variable given its pdf in the vector P
%and the base of the logarithm.  
%P elements must be greater than or equal to zero.

% Copyright (c) 2004-2006 Alessio Botta, Alberto Dainotti, Antonio Pescapè
% Email: {a.botta , alberto , pescape }@unina.it
% DIS - Dipartimento di Informatica e Sistemistica 
% University of Napoli Federico II, ITALY
% All rights reserved.
%
% Redistribution and use in source and binary forms, with or without
% modification, are permitted provided that the following conditions
% are met:
% 1. Redistributions of source code must retain the above copyright
%    notice, this list of conditions and the following disclaimer.
% 2. Redistributions in binary form must reproduce the above copyright
%    notice, this list of conditions and the following disclaimer in the
%    documentation and/or other materials provided with the distribution.
% 3. Redistributions of source code or in binary form must clearly reproduce
%    the reference to the web site from which they were downloaded.
%
% THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
% ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
% IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
% ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
% FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
% DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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% HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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% SUCH DAMAGE.

if (min(P)>=0)
   P = P./sum(P) + (~(P));	
   H = -dot(P,log(P))/log(b);	
else

   disp('ERROR. Negative values found in the input vector')
	
end;