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1 ## Copyright (C) 1996 Auburn University. All rights reserved. |
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2 ## |
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3 ## This file is part of Octave. |
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4 ## |
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5 ## Octave is free software; you can redistribute it and/or modify it |
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6 ## under the terms of the GNU General Public License as published by the |
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7 ## Free Software Foundation; either version 2, or (at your option) any |
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8 ## later version. |
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9 ## |
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10 ## Octave is distributed in the hope that it will be useful, but WITHOUT |
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11 ## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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12 ## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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13 ## for more details. |
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14 ## |
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15 ## You should have received a copy of the GNU General Public License |
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16 ## along with Octave; see the file COPYING. If not, write to the Free |
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17 ## Software Foundation, 59 Temple Place, Suite 330, Boston, MA 02111 USA. |
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18 |
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19 ## -*- texinfo -*- |
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20 ## @deftypefn {Function File} {} tzero (@var{a}, @var{b}, @var{c}, @var{d}@{, @var{opt}@}) |
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21 ## @deftypefnx {Function File} {} tzero (@var{sys}@{,@var{opt}@}) |
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22 ## Compute transmission zeros of a continuous |
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23 ## @example |
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24 ## . |
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25 ## x = Ax + Bu |
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26 ## y = Cx + Du |
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27 ## @end example |
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28 ## or discrete |
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29 ## @example |
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30 ## x(k+1) = A x(k) + B u(k) |
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31 ## y(k) = C x(k) + D u(k) |
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32 ## @end example |
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33 ## system. |
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34 ## @strong{Outputs} |
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35 ## @table @var |
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36 ## @item zer |
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37 ## transmission zeros of the system |
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38 ## @item gain |
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39 ## leading coefficient (pole-zero form) of SISO transfer function |
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40 ## returns gain=0 if system is multivariable |
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41 ## @end table |
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42 ## @strong{References} |
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43 ## @enumerate |
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44 ## @item Emami-Naeini and Van Dooren, Automatica, 1982. |
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45 ## @item Hodel, "Computation of Zeros with Balancing," 1992 Lin. Alg. Appl. |
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46 ## @end enumerate |
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47 ## @end deftypefn |
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48 |
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49 function [zer, gain] = tzero (A, B, C, D) |
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50 |
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51 ## R. Bruce Tenison July 4, 1994 |
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52 ## A. S. Hodel Aug 1995: allow for MIMO and system data structures |
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53 |
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54 ## get A,B,C,D and Asys variables, regardless of initial form |
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55 if(nargin == 4) |
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56 Asys = ss2sys(A,B,C,D); |
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57 elseif( (nargin == 1) && (! is_struct(A))) |
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58 usage("[zer,gain] = tzero(A,B,C,D) or zer = tzero(Asys)"); |
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59 elseif(nargin != 1) |
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60 usage("[zer,gain] = tzero(A,B,C,D) or zer = tzero(Asys)"); |
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61 else |
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62 Asys = A; |
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63 [A,B,C,D] = sys2ss(Asys); |
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60
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64 endif |
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65 |
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66 Ao = Asys; # save for leading coefficient |
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67 siso = is_siso(Asys); |
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68 digital = is_digital(Asys); # check if it's mixed or not |
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69 |
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70 ## see if it's a gain block |
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71 if(isempty(A)) |
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72 zer = []; |
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73 gain = D; |
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74 return; |
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75 endif |
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76 |
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77 ## First, balance the system via the zero computation generalized eigenvalue |
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78 ## problem balancing method (Hodel and Tiller, Linear Alg. Appl., 1992) |
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79 |
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80 Asys = zgpbal(Asys); [A,B,C,D] = sys2ss(Asys); # balance coefficients |
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81 meps = 2*eps*norm([A, B; C, D],'fro'); |
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82 Asys = zgreduce(Asys,meps); [A, B, C, D] = sys2ss(Asys); # ENVD algorithm |
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83 if(!isempty(A)) |
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84 ## repeat with dual system |
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85 Asys = ss2sys(A', C', B', D'); Asys = zgreduce(Asys,meps); |
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86 |
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87 ## transform back |
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88 [A,B,C,D] = sys2ss(Asys); Asys = ss2sys(A', C', B', D'); |
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89 endif |
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90 |
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91 zer = []; # assume none |
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92 [A,B,C,D] = sys2ss(Asys); |
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93 if( !isempty(C) ) |
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94 [W,r,Pi] = qr([C, D]'); |
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95 [nonz,ztmp] = zgrownorm(r,meps); |
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96 if(nonz) |
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97 ## We can now solve the generalized eigenvalue problem. |
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98 [pp,mm] = size(D); |
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99 nn = rows(A); |
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100 Afm = [A , B ; C, D] * W'; |
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101 Bfm = [eye(nn), zeros(nn,mm); zeros(pp,nn+mm)]*W'; |
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102 |
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103 jdx = (mm+1):(mm+nn); |
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104 Af = Afm(1:nn,jdx); |
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105 Bf = Bfm(1:nn,jdx); |
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106 zer = qz(Af,Bf); |
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107 endif |
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108 endif |
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109 |
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110 mz = length(zer); |
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111 [A,B,C,D] = sys2ss(Ao); # recover original system |
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112 ## compute leading coefficient |
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113 if ( (nargout == 2) && siso) |
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114 n = rows(A); |
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115 if ( mz == n) |
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116 gain = D; |
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117 elseif ( mz < n ) |
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118 gain = C*(A^(n-1-mz))*B; |
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119 endif |
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120 else |
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121 gain = []; |
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122 endif |
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123 endfunction |
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124 |
