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diff --git a/modules/cacsd/macros/fspecg.sci b/modules/cacsd/macros/fspecg.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]=fspecg(g)
+    // gm=fspecg(g) : stable factorization.
+    // g and gm are continuous-time linear systems in state-space form.
+    //       gtild(g)*g = gtild(gm)*gm
+    //with gm stable.
+    // Imaginary-axis poles are forbidden.
+    //
+    //!
+    if typeof(g)<>"state-space" then
+        error(msprintf(gettext("%s: Wrong type for input argument #%d: Linear system expected.\n"),"fspecg",1))
+    end
+    if g.dt<>"c" then
+        error(msprintf(gettext("%s: Wrong type for argument #%d: In continuous time expected.\n"),"fspecg",1))
+    end
+
+    [a,b,c,d]=abcd(g),
+    g=[];
+    a=-a;
+    b=-b;
+    h=[-a',c'*c;
+    0*eye(a),a];
+    x=ric_desc(h);h=[]
+    gm=syslin("c",-a'+c'*c*x,-c',b'-d'*c*x,d')';
+endfunction