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