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1 ## Copyright (C) 1996,1998 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{out} =} freqresp (@var{sys},@var{USEW}@{,@var{w}@}); |
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21 ## Frequency response function - used internally by @code{bode}, @code{nyquist}. |
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22 ## minimal argument checking; "do not attempt to do this at home" |
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23 ## |
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24 ## @strong{Inputs} |
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25 ## @table @var |
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26 ## @item sys |
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27 ## system data structure |
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28 ## @item USEW |
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29 ## returned by @code{freqchkw} |
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30 ## @item optional |
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31 ## must be present if @var{USEW} is true (nonzero) |
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32 ## @end table |
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33 ## @strong{Outputs} |
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34 ## @table @var |
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35 ## @item @var{out} |
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36 ## vector of finite @math{G(j*w)} entries (or @math{||G(j*w)||} for MIMO) |
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37 ## @item w |
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38 ## vector of corresponding frequencies |
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39 ## @end table |
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40 ## @end deftypefn |
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41 |
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42 function [ff,w] = freqresp(sys,USEW,w); |
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43 |
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44 ## Written by: R. Bruce Tenison July 11, 1994 |
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45 ## SYS_INTERNAL accesses members of system data structure |
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46 |
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47 save_val = empty_list_elements_ok; |
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48 empty_list_elements_ok = 1; |
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49 |
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50 ## Check Args |
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51 if( (nargin < 2) || (nargin > 4) ) |
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52 usage ("[ff,w] = freqresp(sys,USEW{,w})"); |
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53 elseif( USEW & (nargin < 3) ) |
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54 error("USEW=1 but w was not passed."); |
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55 elseif( USEW & isempty(w)) |
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56 warning("USEW=1 but w is empty; setting USEW=0"); |
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57 USEW=0; |
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58 endif |
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59 |
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60 DIGITAL = is_digital(sys); |
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61 |
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62 ## compute default w if needed |
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63 if(!USEW) |
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64 if(is_siso(sys)) |
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65 sys = sysupdate(sys,"zp"); |
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66 [zer,pol] = sys2zp(sys); |
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67 else |
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68 zer = tzero(sys); |
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69 pol = eig(sys2ss(sys)); |
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70 endif |
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71 |
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72 ## get default frequency range |
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73 [wmin,wmax] = bode_bounds(zer,pol,DIGITAL,sysgettsam(sys)); |
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74 w = logspace(wmin,wmax,50); |
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75 else |
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76 w = reshape(w,1,length(w)); # make sure it's a row vector |
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77 endif |
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78 |
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79 ## now get complex values of s or z |
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80 if(DIGITAL) |
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81 jw = exp(i*w*sysgettsam(sys)); |
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82 else |
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83 jw = i*w; |
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84 endif |
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85 |
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86 [nn,nz,mm,pp] = sysdimensions(sys); |
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87 |
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88 ## now compute the frequency response - divide by zero yields a warning |
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89 if (strcmp(sysgettype(sys),"zp")) |
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90 ## zero-pole form (preferred) |
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91 [zer,pol,sysk] = sys2zp(sys); |
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92 ff = ones(size(jw)); |
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93 l1 = min(length(zer)*(1-isempty(zer)),length(pol)*(1-isempty(pol))); |
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94 for ii=1:l1 |
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95 ff = ff .* (jw - zer(ii)) ./ (jw - pol(ii)); |
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96 endfor |
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97 |
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98 ## require proper transfer function, so now just get poles. |
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99 for ii=(l1+1):length(pol) |
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100 ff = ff ./ (jw - pol(ii)); |
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101 endfor |
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102 ff = ff*sysk; |
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103 |
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104 elseif (strcmp(sysgettype(sys),"tf")) |
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105 ## transfer function form |
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106 [num,den] = sys2tf(sys); |
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107 ff = polyval(num,jw)./polyval(den,jw); |
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108 elseif (mm==pp) |
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109 ## The system is square; do state-space form bode plot |
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110 [sysa,sysb,sysc,sysd,tsam,sysn,sysnz] = sys2ss(sys); |
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111 n = sysn + sysnz; |
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112 for ii=1:length(jw); |
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113 ff(ii) = det(sysc*((jw(ii).*eye(n)-sysa)\sysb)+sysd); |
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114 endfor; |
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115 else |
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116 ## Must be state space... bode |
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117 [sysa,sysb,sysc,sysd,tsam,sysn,sysnz] = sys2ss(sys); |
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118 n = sysn + sysnz; |
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119 for ii=1:length(jw); |
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120 ff(ii) = norm(sysc*((jw(ii)*eye(n)-sysa)\sysb)+sysd); |
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121 endfor |
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122 |
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123 endif |
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124 |
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125 w = reshape(w,1,length(w)); |
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126 ff = reshape(ff,1,length(ff)); |
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127 |
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128 ## restore global variable |
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129 empty_list_elements_ok = save_val; |
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130 endfunction |
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131 |
