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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, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
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18 ## 02110-1301 USA. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {} starp (@var{P}, @var{K}, @var{ny}, @var{nu}) |
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22 ## |
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23 ## Redheffer star product or upper/lower LFT, respectively. |
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24 ## @example |
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25 ## @group |
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26 ## |
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27 ## +-------+ |
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28 ## --------->| |---------> |
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29 ## | P | |
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30 ## +--->| |---+ ny |
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31 ## | +-------+ | |
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32 ## +-------------------+ |
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33 ## | | |
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34 ## +----------------+ | |
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35 ## | | |
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36 ## | +-------+ | |
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37 ## +--->| |------+ nu |
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38 ## | K | |
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39 ## --------->| |---------> |
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40 ## +-------+ |
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41 ## @end group |
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42 ## @end example |
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43 ## If @var{ny} and @var{nu} ``consume'' all inputs and outputs of |
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44 ## @var{K} then the result is a lower fractional transformation. |
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45 ## If @var{ny} and @var{nu} ``consume'' all inputs and outputs of |
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46 ## @var{P} then the result is an upper fractional transformation. |
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47 ## |
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48 ## @var{ny} and/or @var{nu} may be negative (i.e. negative feedback). |
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49 ## @end deftypefn |
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50 |
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51 ## Author: Kai P. Mueller <mueller@ifr.ing.tu-bs.de> |
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52 ## Created: May 1998 |
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53 |
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54 function sys = starp (P, K, ny, nu); |
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55 |
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56 if((nargin != 2) && (nargin != 4)) |
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57 usage("sys = starp(P, K, ny, nu)"); |
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58 endif |
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59 if (!isstruct(P)) |
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60 error("---> P must be in system data structure"); |
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61 endif |
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62 if (!isstruct(K)) |
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63 error("---> K must be in system data structure"); |
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64 endif |
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65 |
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66 P = sysupdate(P, "ss"); |
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67 [n, nz, mp, pp] = sysdimensions(P); |
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68 np = n + nz; |
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69 K = sysupdate(K, "ss"); |
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70 [n, nz, mk, pk] = sysdimensions(K); |
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71 nk = n + nz; |
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72 ny_sign = 1; |
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73 nu_sign = 1; |
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74 if (nargin == 2) |
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75 ## perform a LFT of P and K (upper or lower) |
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76 ny = min([pp, mk]); |
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77 nu = min([pk, mp]); |
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78 else |
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79 if (ny < 0) |
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80 ny = -ny; |
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81 ny_sign = -1; |
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82 endif |
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83 if (nu < 0) |
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84 nu = -nu; |
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85 nu_sign = -1; |
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86 endif |
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87 endif |
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88 if (ny > pp) |
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89 error("---> P has not enough outputs."); |
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90 endif |
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91 if (nu > mp) |
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92 error("---> P has not enough inputs."); |
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93 endif |
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94 if (ny > mk) |
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95 error("---> K has not enough inputs."); |
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96 endif |
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97 if (nu > pk) |
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98 error("---> K has not enough outputs."); |
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99 endif |
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100 nwp = mp - nu; |
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101 nzp = pp - ny; |
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102 nwk = mk - ny; |
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103 nzk = pk - nu; |
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104 if ((nwp + nwk) < 1) |
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105 error("---> no inputs left for star product."); |
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106 endif |
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107 if ((nzp + nzk) < 1) |
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108 error("---> no outputs left for star product."); |
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109 endif |
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110 |
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111 ## checks done, form sys |
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112 if (nzp) Olst = [1:nzp]; endif |
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113 if (nzk) Olst = [Olst, pp+nu+1:pp+pk]; endif |
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114 if (nwp) Ilst = [1:nwp]; endif |
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115 if (nwk) Ilst = [Ilst, mp+ny+1:mp+mk]; endif |
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116 Clst = zeros(ny+nu,2); |
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117 for ii = 1:nu |
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118 Clst(ii,:) = [nwp+ii, nu_sign*(pp+ii)]; |
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119 endfor |
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120 for ii = 1:ny |
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121 Clst(nu+ii,:) = [mp+ii, ny_sign*(nzp+ii)]; |
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122 endfor |
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123 sys = buildssic(Clst,[],Olst,Ilst,P,K); |
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124 |
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125 endfunction |
