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// Scilab ( http://www.scilab.org/ ) - This file is part of Scilab
// Copyright (C) INRIA -
//
// This file must be used under the terms of the CeCILL.
// This source file is licensed as described in the file COPYING, which
// you should have received as part of this distribution. The terms
// are also available at
// http://www.cecill.info/licences/Licence_CeCILL_V2.1-en.txt
function [enx,X,Y,eny]=entropy(S,gama)
//Computation of the entropy at gama of a linear system S
//[enx,X,Y,eny]=entropy(S,gama)
//!
//
S1=S(1);
if S1(1)=="r" then S=tf2ss(S);end
[A,B,C,D]=S(2:5);
g1=1/gama;
H=[A,g1*B*B';-g1*C'*C,-A'];
[X,zero]=ric_desc(H); //zero=A'*X+X*A+g1*g1*X*B*B'*X+C'*C;
enx=sum(diag(X*B*B'));
J=[A',g1*C'*C;-g1*B*B',-A];
[Y,zero]=ric_desc(J); //zero=A*Y+Y*A'+g1*g1*Y*C'*C*Y+B*B'
eny=sum(diag(Y*C'*C));
endfunction
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