// 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