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diff --git a/modules/cacsd/macros/entropy.sci b/modules/cacsd/macros/entropy.sci
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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