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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} {} syssub (@var{Gsys}, @var{Hsys}) |
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21 ## returns @math{sys = Gsys - Hsys} |
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22 ## |
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23 ## Method: @var{Gsys} and @var{Hsys} are connected in parallel |
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24 ## The input vector is connected to both systems; the outputs are |
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25 ## subtracted. Returned system names are those of @var{Gsys}. |
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26 ## @example |
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27 ## @group |
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28 ## +--------+ |
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29 ## +--->| Gsys |---+ |
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30 ## | +--------+ | |
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31 ## | +| |
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32 ## u --+ (_)--> y |
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33 ## | -| |
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34 ## | +--------+ | |
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35 ## +--->| Hsys |---+ |
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36 ## +--------+ |
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37 ## @end group |
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38 ## @end example |
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39 ## @end deftypefn |
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40 |
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41 ## Author: John Ingram <ingraje@eng.auburn.edu> |
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42 ## Created: July 1996 |
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43 ## updated for variable numbers of input arguments by July 1999 A. S. Hodel |
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44 |
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45 function sys = syssub (...) |
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46 |
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47 if(nargin < 1) |
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48 usage("syssub: sys = syssub(Gsys{,Hsys,...})"); |
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49 endif |
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50 |
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51 ## collect all arguments |
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52 arglist = list(); |
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53 va_start(); |
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54 for kk=1:nargin |
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55 arglist(kk) = va_arg(); |
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56 if(!is_struct(nth(arglist,kk))) |
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57 error("syssub: argument %d is not a data structure",kk); |
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58 endif |
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59 endfor |
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60 |
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61 ## check system dimensions |
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62 [n,nz,mg,pg,Gyd] = sysdimensions(nth(arglist,1)); |
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63 for kk=2:nargin |
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64 [n,nz,mh,ph,Hyd] = sysdimensions(nth(arglist,kk)); |
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65 if(mg != mh) |
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66 error("arg 1 has %d inputs; arg %d has vs %d inputs",mg,kk,mh); |
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67 elseif(pg != ph) |
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68 error("arg 1 has %d outputs; arg %d has vs %d outputs",pg,kk,ph); |
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69 elseif(norm(Gyd - Hyd)) |
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70 warning("cannot add a discrete output to a continuous output"); |
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71 error("Output type mismatch: arguments 1 and %d\n",kk); |
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72 endif |
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73 endfor |
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74 |
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75 ## perform the subtract |
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76 if(nargin == 2) |
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77 Gsys = nth(arglist,1); Hsys = nth(arglist,2); |
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78 if( strcmp(sysgettype(Gsys),"tf") | strcmp(sysgettype(Hsys),"tf") ) |
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79 ## see if subtracting transfer functions with identical denominators |
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80 [Gnum,Gden,GT,Gin,Gout] = sys2tf(Gsys); |
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81 [Hnum,Hden,HT,Hin,Hout] = sys2tf(Hsys); |
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82 if(length(Hden) == length(Gden) ) |
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83 if( (Hden == Gden) & (HT == GT) ) |
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84 sys = tf2sys(Gnum+Hnum,Gden,GT,Gin,Gout); |
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85 return |
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86 endif |
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87 ## if not, we go on and do the usual thing... |
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88 endif |
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89 endif |
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90 |
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91 ## make sure in ss form |
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92 Gsys = sysupdate(Gsys,"ss"); |
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93 Hsys = sysupdate(Hsys,"ss"); |
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94 |
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95 ## change signal names to avoid warning messages from sysgroup |
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96 Gsys = syssetsignals(Gsys,"in",__sysdefioname__(length(Gin),"Gin_u")); |
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97 Gsys = syssetsignals(Gsys,"out",__sysdefioname__(length(Gout),"Gout_u")); |
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98 Hsys = syssetsignals(Hsys,"in",__sysdefioname__(length(Hin),"Hin_u")); |
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99 Hsys = syssetsignals(Hsys,"out",__sysdefioname__(length(Hout),"Hout_u")); |
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100 |
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101 sys = sysgroup(Gsys,Hsys); |
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102 |
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103 eyin = eye(mg); |
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104 eyout = eye(pg); |
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105 |
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106 sys = sysscale (sys, [eyout, -eyout], [eyin; eyin], Gout, Gin); |
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107 |
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108 else |
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109 ## multiple systems (or a single system); combine together one by one |
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110 sys = nth(arglist,1); |
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111 for kk=2:length(arglist) |
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112 sys = syssub(sys,nth(arglist,kk)); |
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113 endfor |
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114 endif |
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115 |
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116 endfunction |
