function[result]=joint_ent(Pb,b)
% Calculate the joint entropy of the bivariate 
% probability ditribution Pb
%

% 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.
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% 2. Redistributions in binary form must reproduce the above copyright
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%    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.
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Qb=Pb;
sizeP=size(Pb);
for i1=1:1:sizeP(1,1)
  for i2=1:1:sizeP(1,2)
    if Qb(i1,i2)==0.0  Qb(i1,i2)=1; end;
  end;
end;
Rb=-Pb.*(log10(Qb)./log10(b));
Cs=sum(Rb);
result=sum(Cs);