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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 |
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7 ## the Free Software Foundation; either version 3 of the License, or (at |
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8 ## your option) any later version. |
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9 ## |
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10 ## Octave is distributed in the hope that it will be useful, but |
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of |
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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13 ## General Public License 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, see |
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17 ## <http://www.gnu.org/licenses/>. |
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18 |
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19 ## Undocumented internal function. |
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20 |
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21 ## -*- texinfo -*- |
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22 ## @deftypefn {Function File} {} __freqresp__ (@var{sys}, @var{USEW}, @var{w}) |
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23 ## Frequency response function - used internally by @command{bode}, @command{nyquist}. |
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24 ## minimal argument checking; ``do not attempt to do this at home''. |
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25 ## |
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26 ## @strong{Inputs} |
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27 ## @table @var |
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28 ## @item sys |
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29 ## system data structure |
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30 ## @item USEW |
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31 ## returned by @code{freqchkw} |
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32 ## @item optional |
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33 ## must be present if @var{USEW} is true (nonzero) |
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34 ## @end table |
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35 ## @strong{Outputs} |
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36 ## @table @var |
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37 ## @item @var{out} |
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38 ## vector of finite @math{G(j*w)} entries (or @math{||G(j*w)||} for @acronym{MIMO}) |
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39 ## @item w |
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40 ## vector of corresponding frequencies |
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41 ## @end table |
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42 ## @end deftypefn |
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43 |
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44 ## Author: R. Bruce Tenison <btenison@eng.auburn.edu> |
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45 ## Created: July 11, 1994 |
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46 |
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47 function [ff, w] = __freqresp__ (sys, USEW, w); |
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48 |
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49 ## SYS_INTERNAL accesses members of system data structure |
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50 |
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51 ## Check Args |
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52 if ((nargin < 2) || (nargin > 4)) |
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53 print_usage (); |
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54 elseif (USEW & (nargin < 3) ) |
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55 error ("USEW = 1 but w was not passed."); |
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56 elseif (USEW & isempty(w)) |
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57 warning("USEW = 1 but w is empty; setting USEW=0"); |
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58 USEW = 0; |
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59 endif |
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60 |
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61 DIGITAL = is_digital(sys); |
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62 |
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63 ## compute default w if needed |
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64 if(!USEW) |
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65 if(is_siso(sys)) |
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66 sys = sysupdate(sys,"zp"); |
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67 [zer,pol] = sys2zp(sys); |
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68 else |
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69 zer = tzero(sys); |
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70 pol = eig(sys2ss(sys)); |
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71 endif |
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72 |
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73 ## get default frequency range |
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74 [wmin,wmax] = bode_bounds(zer,pol,DIGITAL,sysgettsam(sys)); |
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75 w = logspace(wmin,wmax,50); |
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76 else |
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77 w = reshape(w,1,length(w)); # make sure it's a row vector |
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78 endif |
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79 |
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80 ## now get complex values of s or z |
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81 if(DIGITAL) |
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82 jw = exp(i*w*sysgettsam(sys)); |
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83 else |
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84 jw = i*w; |
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85 endif |
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86 |
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87 [nn,nz,mm,pp] = sysdimensions(sys); |
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88 |
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89 ## now compute the frequency response - divide by zero yields a warning |
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90 if (strcmp(sysgettype(sys),"zp")) |
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91 ## zero-pole form (preferred) |
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92 [zer,pol,sysk] = sys2zp(sys); |
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93 ff = ones(size(jw)); |
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94 l1 = min(length(zer)*(1-isempty(zer)),length(pol)*(1-isempty(pol))); |
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95 for ii=1:l1 |
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96 ff = ff .* (jw - zer(ii)) ./ (jw - pol(ii)); |
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97 endfor |
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98 |
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99 ## require proper transfer function, so now just get poles. |
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100 for ii=(l1+1):length(pol) |
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101 ff = ff ./ (jw - pol(ii)); |
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102 endfor |
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103 ff = ff*sysk; |
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104 |
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105 elseif (strcmp(sysgettype(sys),"tf")) |
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106 ## transfer function form |
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107 [num,den] = sys2tf(sys); |
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108 ff = polyval(num,jw)./polyval(den,jw); |
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109 elseif (mm==pp) |
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110 ## The system is square; do state-space form bode plot |
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111 [sysa,sysb,sysc,sysd,tsam,sysn,sysnz] = sys2ss(sys); |
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112 n = sysn + sysnz; |
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113 for ii=1:length(jw); |
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114 ff(ii) = det(sysc*((jw(ii).*eye(n)-sysa)\sysb)+sysd); |
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115 endfor; |
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116 else |
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117 ## Must be state space... bode |
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118 [sysa,sysb,sysc,sysd,tsam,sysn,sysnz] = sys2ss(sys); |
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119 n = sysn + sysnz; |
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120 for ii=1:length(jw); |
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121 ff(ii) = norm(sysc*((jw(ii)*eye(n)-sysa)\sysb)+sysd); |
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122 endfor |
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123 |
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124 endif |
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125 |
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126 w = reshape(w,1,length(w)); |
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127 ff = reshape(ff,1,length(ff)); |
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128 |
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129 endfunction |
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130 |
