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1 ## Copyright (C) 1996, 1999, 2000, 2002, 2004, 2005, 2006, 2007 |
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2 ## Auburn University. All rights reserved. |
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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{sys} =} syssub (@var{Gsys}, @var{Hsys}) |
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22 ## Return @math{sys = Gsys - Hsys}. |
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23 ## |
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24 ## @strong{Method} |
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25 ## |
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26 ## @var{Gsys} and @var{Hsys} are connected in parallel. |
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27 ## The input vector is connected to both systems; the outputs are |
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28 ## subtracted. Returned system names are those of @var{Gsys}. |
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29 ## @example |
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30 ## @group |
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31 ## +--------+ |
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32 ## +--->| Gsys |---+ |
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33 ## | +--------+ | |
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34 ## | +| |
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35 ## u --+ (_)--> y |
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36 ## | -| |
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37 ## | +--------+ | |
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38 ## +--->| Hsys |---+ |
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39 ## +--------+ |
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40 ## @end group |
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41 ## @end example |
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42 ## @end deftypefn |
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43 |
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44 ## Author: John Ingram <ingraje@eng.auburn.edu> |
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45 ## Created: July 1996 |
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46 ## updated for variable numbers of input arguments by July 1999 A. S. Hodel |
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47 |
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48 function sys = syssub (varargin) |
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49 |
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50 if (nargin < 1) |
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51 print_usage (); |
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52 endif |
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53 |
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54 ## collect all arguments |
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55 arglist = {}; |
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56 for kk = 1:nargin |
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57 arglist{kk} = varargin{kk}; |
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58 if (! isstruct (arglist{kk})) |
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59 error ("syssub: argument %d is not a data structure", kk); |
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60 endif |
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61 endfor |
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62 |
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63 ## check system dimensions |
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64 [n, nz, mg, pg, Gyd] = sysdimensions (arglist{1}); |
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65 for kk = 2:nargin |
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66 [n, nz, mh, ph, Hyd] = sysdimensions (arglist{kk}); |
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67 if (mg != mh) |
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68 error ("arg 1 has %d inputs; arg %d has vs %d inputs", mg, kk, mh); |
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69 elseif (pg != ph) |
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70 error ("arg 1 has %d outputs; arg %d has vs %d outputs", pg, kk, ph); |
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71 elseif (norm (Gyd - Hyd)) |
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72 warning ("cannot add a discrete output to a continuous output"); |
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73 error ("Output type mismatch: arguments 1 and %d", kk); |
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74 endif |
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75 endfor |
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76 |
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77 ## perform the subtract |
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78 if (nargin == 2) |
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79 Gsys = arglist{1}; |
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80 Hsys = arglist{2}; |
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81 if (strcmp (sysgettype (Gsys), "tf") || strcmp (sysgettype (Hsys), "tf")) |
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82 ## see if subtracting transfer functions with identical denominators |
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83 [Gnum, Gden, GT, Gin, Gout] = sys2tf (Gsys); |
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84 [Hnum, Hden, HT, Hin, Hout] = sys2tf (Hsys); |
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85 if (length (Hden) == length (Gden)) |
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86 if ((Hden == Gden) & (HT == GT)) |
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87 sys = tf (Gnum-Hnum, Gden, GT, Gin, Gout); |
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88 return; |
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89 endif |
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90 ## if not, we go on and do the usual thing... |
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91 endif |
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92 endif |
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93 |
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94 ## make sure in ss form |
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95 Gsys = sysupdate (Gsys, "ss"); |
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96 Hsys = sysupdate (Hsys, "ss"); |
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97 |
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98 ## change signal names to avoid warning messages from sysgroup |
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99 Gsys = syssetsignals (Gsys, "in", |
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100 __sysdefioname__(length(Gin), "Gin_u")); |
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101 |
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102 Gsys = syssetsignals (Gsys, "out", |
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103 __sysdefioname__(length(Gout), "Gout_u")); |
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104 |
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105 Hsys = syssetsignals (Hsys, "in", |
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106 __sysdefioname__(length(Hin), "Hin_u")); |
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107 |
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108 Hsys = syssetsignals (Hsys, "out", |
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109 __sysdefioname__(length(Hout), "Hout_u")); |
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110 |
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111 sys = sysgroup (Gsys, Hsys); |
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112 |
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113 eyin = eye (mg); |
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114 eyout = eye (pg); |
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115 |
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116 sys = sysscale (sys, [eyout, -eyout], [eyin; eyin], Gout, Gin); |
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117 |
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118 else |
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119 ## multiple systems (or a single system); combine together one by one |
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120 sys = arglist{1}; |
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121 for kk = 2:length(arglist) |
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122 sys = syssub (sys, arglist{kk}); |
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123 endfor |
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124 endif |
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125 |
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126 endfunction |
