1 ## Copyright (C) 2009, 2011 Lukas F. Reichlin
3 ## This file is part of LTI Syncope.
5 ## LTI Syncope is free software: you can redistribute it and/or modify
6 ## it under the terms of the GNU General Public License as published by
7 ## the Free Software Foundation, either version 3 of the License, or
8 ## (at your option) any later version.
10 ## LTI Syncope is distributed in the hope that it will be useful,
11 ## but WITHOUT ANY WARRANTY; without even the implied warranty of
12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 ## GNU General Public License for more details.
15 ## You should have received a copy of the GNU General Public License
16 ## along with LTI Syncope. If not, see <http://www.gnu.org/licenses/>.
19 ## Inversion of TF models.
21 ## Author: Lukas Reichlin <lukas.reichlin@gmail.com>
22 ## Created: October 2009
25 function sys = __sys_inverse__ (sys)
31 if (all (nvec == 1)) # SISO
32 if (num{1,1} == 0) # catch case num = 0
33 sys.num(1,1) = tfpoly (0);
34 sys.den(1,1) = tfpoly (1);
39 elseif (all (nvec == 2)) # 2x2 MIMO
40 sys.num(1,1) = -den{1,1}*den{1,2}*den{2,1}*num{2,2};
41 sys.num(1,2) = den{1,1}*den{2,1}*den{2,2}*num{1,2};
42 sys.num(2,1) = den{1,1}*den{1,2}*den{2,2}*num{2,1};
43 sys.num(2,2) = -den{1,2}*den{2,1}*den{2,2}*num{1,1};
44 sys.den(:) = den{1,1}*den{2,2}*num{1,2}*num{2,1} - den{1,2}*den{2,1}*num{1,1}*num{2,2};
46 ## I've calculated 3x3 systems with sage but the formula is quite long
47 [num, den] = tfdata (inv (ss (sys)), "tfpoly");