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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 [s1]=cls2dls(s,t,fp)
//Syntax : s1=cls2dls(sl,t [,fp])
//
// Given sl=[a,b,c,d] (syslin list) continuous time system, cls2dls
// returns the sampled system obatined by the bilinear transform
// s=(2/t)*(z-1)/(z+1).
//
// t sampling period
// fp prevarping frequency in hertz
//!
[lhs,rhs]=argn(0)
if typeof(s)<>"state-space"
error(msprintf(gettext("%s: Wrong type for input argument #%d: Linear state space expected.\n"),"cls2dls",1))
end
if s.dt==[] then
warning(msprintf(gettext("%s: Input argument %d is assumed continuous time.\n"),"cls2dls",1));
s.dt="c";
end
if s.dt<>"c" then
error(msprintf(gettext("%s: Wrong value for input argument #%d: Continuous time system expected.\n"),"cls2dls",1))
end
fs=1/t
if rhs==3 then fp=2*%pi*fp;fs=fp/tan(fp/fs/2)/2,end //prewarping
a=2*fs*eye()-s(2)
ad=a\(2*fs*eye()+s(2))
b=(ad+eye())/a*s(3);
d=s(5)+s(4)/a*s(3)
s1=syslin("d",ad,b,s(4),d,s(6))
endfunction
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