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diff --git a/modules/cacsd/macros/cfspec.sci b/modules/cacsd/macros/cfspec.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 [gm]=cfspec(g)
+    //[gm]=cfspec(g) computes a co-spectral factorization:
+    //        g = gm*gtild(gm)
+    //with stable gm and gm^-1  ( gm^-1 = invsyslin(gm) ).
+    //-- g: syslin list defining the linear system g
+    //-- gm:
+    //Assumptions:
+    //- g is invertible ( inv(D) exists ),
+    //- g and g^1 (invsyslin(g)) have no poles on the imaginary axis.
+    //- gtild(g) = g.
+    //  (poles and zeros of g are symmetric wrt imaginary axis))
+    //- g(+oo) = D is positive definite.
+    //!
+
+    if type(g)==1 then gm=chol(g),return,end,
+    gm=fspec(g'),
+    gm=gm'
+endfunction