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1 ## Copyright (C) 1998, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007 |
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2 ## Kai P. Mueller. |
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3 ## |
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4 ## This file is part of Octave. |
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5 ## |
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6 ## Octave is free software; you can redistribute it and/or modify it |
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7 ## under the terms of the GNU General Public License as published by |
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8 ## the Free Software Foundation; either version 3 of the License, or (at |
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9 ## your option) any later version. |
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10 ## |
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11 ## Octave is distributed in the hope that it will be useful, but |
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12 ## WITHOUT ANY WARRANTY; without even the implied warranty of |
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13 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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14 ## General Public License for more details. |
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15 ## |
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16 ## You should have received a copy of the GNU General Public License |
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17 ## along with Octave; see the file COPYING. If not, see |
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18 ## <http://www.gnu.org/licenses/>. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {@var{retval} =} is_stabilizable (@var{sys}, @var{tol}) |
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22 ## @deftypefnx {Function File} {@var{retval} =} is_stabilizable (@var{a}, @var{b}, @var{tol}, @var{dflg}) |
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23 ## Logical check for system stabilizability (i.e., all unstable modes are controllable). |
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24 ## Returns 1 if the system is stabilizable, 0 if the system is not stabilizable, -1 |
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25 ## if the system has non stabilizable modes at the imaginary axis (unit circle for |
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26 ## discrete-time systems. |
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27 ## |
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28 ## Test for stabilizability is performed via Hautus Lemma. If |
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29 ## @iftex |
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30 ## @tex |
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31 ## @var{dflg}$\neq$0 |
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32 ## @end tex |
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33 ## @end iftex |
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34 ## @ifinfo |
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35 ## @var{dflg}!=0 |
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36 ## @end ifinfo |
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37 ## assume that discrete-time matrices (a,b) are supplied. |
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38 ## @seealso{size, rows, columns, length, ismatrix, isscalar, isvector |
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39 ## is_observable, is_stabilizable, is_detectable} |
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40 ## @end deftypefn |
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41 |
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42 ## Author: A. S. Hodel <a.s.hodel@eng.auburn.edu> |
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43 ## Created: August 1993 |
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44 ## Updated by A. S. Hodel (scotte@eng.auburn.edu) Aubust, 1995 to use krylovb |
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45 ## Updated by John Ingram (ingraje@eng.auburn.edu) July, 1996 to accept systems |
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46 |
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47 function retval = is_stabilizable (a, b, tol, dflg) |
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48 |
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49 if (nargin < 1) |
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50 print_usage (); |
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51 elseif (isstruct (a)) |
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52 ## system passed. |
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53 if (nargin == 2) |
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54 tol = b; % get tolerance |
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55 elseif (nargin > 2) |
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56 print_usage (); |
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57 endif |
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58 disc = is_digital(a); |
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59 [a, b] = sys2ss (a); |
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60 else |
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61 ## a,b arguments sent directly. |
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62 if (nargin > 4 || nargin == 1) |
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63 print_usage (); |
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64 endif |
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65 if (exist ("dflg")) |
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66 disc = dflg; |
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67 else |
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68 disc = 0; |
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69 end |
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70 endif |
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71 |
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72 if (! exist ("tol")) |
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73 tol = 200*eps; |
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74 endif |
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75 |
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76 |
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77 ## Checking dimensions |
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78 n = is_square (a); |
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79 if (n == 0) |
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80 error ("is_stabilizable: a must be square"); |
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81 endif |
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82 [nr, m] = size (b); |
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83 if (nr != n) |
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84 error ("is_stabilizable: (a,b) not conformal"); |
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85 endif |
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86 |
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87 ##Computing the eigenvalue of A |
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88 L = eig (a); |
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89 retval = 1; |
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90 specflag = 0; |
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91 for i = 1:n |
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92 if (disc == 0) |
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93 ## Continuous time case |
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94 rL = real (L(i)); |
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95 if (rL >= 0) |
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96 H = [eye(n)*L(i)-a, b]; |
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97 f = (rank (H, tol) == n); |
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98 if (f == 0) |
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99 retval = 0; |
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100 if (rL == 0) |
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101 specflag = 1; |
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102 endif |
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103 endif |
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104 endif |
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105 else |
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106 ## Discrete time case |
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107 rL = abs (L(i)); |
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108 if (rL >= 1) |
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109 H = [eye(n)*L(i)-a, b]; |
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110 f = (rank (H, tol) == n); |
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111 if (f == 0) |
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112 retval = 0; |
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113 if (rL == 1) |
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114 specflag = 1; |
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115 endif |
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116 endif |
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117 endif |
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118 endif |
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119 endfor |
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120 if (specflag == 1) |
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121 ## This means that the system has uncontrollable modes at the imaginary axis |
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122 ## (or at the unit circle for discrete time systems) |
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123 retval = -1; |
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124 endif |
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125 |
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126 endfunction |
