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1 ## Copyright (C) 1996, 1998, 2000, 2003, 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 ## Undocumented internal function. |
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21 |
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22 ## -*- texinfo -*- |
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23 ## @deftypefn {Function File} {} __freqresp__ (@var{sys}, @var{USEW}, @var{w}) |
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24 ## Frequency response function - used internally by @command{bode}, @command{nyquist}. |
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25 ## minimal argument checking; ``do not attempt to do this at home''. |
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26 ## |
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27 ## @strong{Inputs} |
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28 ## @table @var |
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29 ## @item sys |
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30 ## system data structure |
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31 ## @item USEW |
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32 ## returned by @code{freqchkw} |
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33 ## @item optional |
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34 ## must be present if @var{USEW} is true (nonzero) |
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35 ## @end table |
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36 ## @strong{Outputs} |
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37 ## @table @var |
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38 ## @item @var{out} |
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39 ## vector of finite @math{G(j*w)} entries (or @math{||G(j*w)||} for @acronym{MIMO}) |
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40 ## @item w |
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41 ## vector of corresponding frequencies |
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42 ## @end table |
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43 ## @end deftypefn |
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44 |
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45 ## Author: R. Bruce Tenison <btenison@eng.auburn.edu> |
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46 ## Created: July 11, 1994 |
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47 |
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48 function [ff, w] = __freqresp__ (sys, USEW, w); |
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49 |
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50 ## SYS_INTERNAL accesses members of system data structure |
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51 |
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52 ## Check Args |
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53 if (nargin < 2 || nargin > 4) |
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54 print_usage (); |
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55 elseif (USEW && nargin < 3) |
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56 error ("USEW = 1 but w was not passed."); |
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57 elseif (USEW && isempty (w)) |
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58 warning ("USEW = 1 but w is empty; setting USEW=0"); |
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59 USEW = 0; |
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60 endif |
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61 |
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62 DIGITAL = is_digital (sys); |
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63 |
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64 ## compute default w if needed |
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65 if (! USEW) |
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66 if (is_siso (sys)) |
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67 sys = sysupdate (sys, "zp"); |
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68 [zer, pol] = sys2zp (sys); |
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69 else |
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70 zer = tzero (sys); |
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71 pol = eig (sys2ss (sys)); |
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72 endif |
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73 |
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74 ## get default frequency range |
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75 [wmin, wmax] = bode_bounds (zer, pol, DIGITAL, sysgettsam (sys)); |
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76 w = logspace (wmin, wmax, 50); |
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77 else |
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78 w = reshape (w, 1, length (w)); # make sure it's a row vector |
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79 endif |
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80 |
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81 ## now get complex values of s or z |
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82 if (DIGITAL) |
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83 jw = exp (i*w*sysgettsam(sys)); |
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84 else |
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85 jw = i*w; |
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86 endif |
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87 |
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88 [nn, nz, mm, pp] = sysdimensions (sys); |
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89 |
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90 ## now compute the frequency response - divide by zero yields a warning |
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91 if (strcmp (sysgettype (sys), "zp")) |
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92 ## zero-pole form (preferred) |
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93 [zer, pol, sysk] = sys2zp (sys); |
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94 ff = ones (size (jw)); |
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95 l1 = min (length(zer)*(1-isempty(zer)), length(pol)*(1-isempty(pol))); |
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96 for ii = 1:l1 |
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97 ff = ff .* (jw - zer(ii)) ./ (jw - pol(ii)); |
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98 endfor |
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99 |
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100 ## require proper transfer function, so now just get poles. |
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101 for ii = (l1+1):length(pol) |
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102 ff = ff ./ (jw - pol(ii)); |
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103 endfor |
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104 ff = ff*sysk; |
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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 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 endfunction |
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129 |
