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1 ## Copyright (C) 1996, 1999 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} {@var{sys} =} syssub (@var{Gsys}, @var{Hsys}) |
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21 ## Return @math{sys = Gsys - Hsys}. |
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22 ## |
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23 ## @strong{Method} |
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24 ## |
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25 ## @var{Gsys} and @var{Hsys} are connected in parallel. |
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26 ## The input vector is connected to both systems; the outputs are |
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27 ## subtracted. Returned system names are those of @var{Gsys}. |
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28 ## @example |
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29 ## @group |
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30 ## +--------+ |
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31 ## +--->| Gsys |---+ |
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32 ## | +--------+ | |
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33 ## | +| |
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34 ## u --+ (_)--> y |
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35 ## | -| |
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36 ## | +--------+ | |
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37 ## +--->| Hsys |---+ |
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38 ## +--------+ |
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39 ## @end group |
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40 ## @end example |
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41 ## @end deftypefn |
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42 |
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43 ## Author: John Ingram <ingraje@eng.auburn.edu> |
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44 ## Created: July 1996 |
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45 ## updated for variable numbers of input arguments by July 1999 A. S. Hodel |
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46 |
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47 function sys = syssub (varargin) |
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48 |
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49 if(nargin < 1) |
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50 usage("syssub: sys = syssub(Gsys{,Hsys,...})"); |
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51 endif |
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52 |
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53 ## collect all arguments |
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54 arglist = {}; |
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55 for kk=1:nargin |
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56 arglist{kk} = varargin{kk}; |
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57 if(!isstruct(arglist{kk})) |
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58 error("syssub: argument %d is not a data structure",kk); |
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59 endif |
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60 endfor |
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61 |
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62 ## check system dimensions |
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63 [n,nz,mg,pg,Gyd] = sysdimensions(arglist{1}); |
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64 for kk=2:nargin |
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65 [n,nz,mh,ph,Hyd] = sysdimensions(arglist{kk}); |
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66 if(mg != mh) |
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67 error("arg 1 has %d inputs; arg %d has vs %d inputs",mg,kk,mh); |
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68 elseif(pg != ph) |
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69 error("arg 1 has %d outputs; arg %d has vs %d outputs",pg,kk,ph); |
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70 elseif(norm(Gyd - Hyd)) |
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71 warning("cannot add a discrete output to a continuous output"); |
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72 error("Output type mismatch: arguments 1 and %d\n",kk); |
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73 endif |
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74 endfor |
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75 |
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76 ## perform the subtract |
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77 if(nargin == 2) |
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78 Gsys = arglist{1}; |
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79 Hsys = arglist{2}; |
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80 if( strcmp(sysgettype(Gsys),"tf") | strcmp(sysgettype(Hsys),"tf") ) |
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81 ## see if subtracting transfer functions with identical denominators |
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82 [Gnum,Gden,GT,Gin,Gout] = sys2tf(Gsys); |
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83 [Hnum,Hden,HT,Hin,Hout] = sys2tf(Hsys); |
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84 if(length(Hden) == length(Gden) ) |
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85 if( (Hden == Gden) & (HT == GT) ) |
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86 sys = tf(Gnum-Hnum,Gden,GT,Gin,Gout); |
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87 return |
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88 endif |
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89 ## if not, we go on and do the usual thing... |
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90 endif |
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91 endif |
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92 |
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93 ## make sure in ss form |
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94 Gsys = sysupdate(Gsys,"ss"); |
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95 Hsys = sysupdate(Hsys,"ss"); |
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96 |
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97 ## change signal names to avoid warning messages from sysgroup |
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98 Gsys = syssetsignals(Gsys,"in",__sysdefioname__(length(Gin),"Gin_u")); |
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99 Gsys = syssetsignals(Gsys,"out",__sysdefioname__(length(Gout),"Gout_u")); |
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100 Hsys = syssetsignals(Hsys,"in",__sysdefioname__(length(Hin),"Hin_u")); |
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101 Hsys = syssetsignals(Hsys,"out",__sysdefioname__(length(Hout),"Hout_u")); |
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102 |
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103 sys = sysgroup(Gsys,Hsys); |
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104 |
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105 eyin = eye(mg); |
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106 eyout = eye(pg); |
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107 |
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108 sys = sysscale (sys, [eyout, -eyout], [eyin; eyin], Gout, Gin); |
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109 |
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110 else |
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111 ## multiple systems (or a single system); combine together one by one |
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112 sys = arglist{1}; |
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113 for kk=2:length(arglist) |
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114 sys = syssub(sys,arglist{kk}); |
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115 endfor |
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116 endif |
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117 |
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118 endfunction |
