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1 # Copyright (C) 1998 A. Scottedward Hodel |
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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, 675 Mass Ave, Cambridge, MA 02139, USA. |
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18 |
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19 function [mag,phase,w] = nichols(sys,w,outputs,inputs) |
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20 # [mag,phase,w] = nichols(sys[,w,outputs,inputs]) |
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21 # Produce Nichols plot of a system |
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22 # |
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23 # Compute the frequency response of a system. |
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24 # inputs: |
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25 # sys: system data structure (must be either purely continuous or discrete; |
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26 # see is_digital) |
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27 # w: frequency values for evaluation. |
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28 # if sys is continuous, then nichols evaluates G(jw) |
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29 # if sys is discrete, then nichols evaluates G(exp(jwT)), where T=sys.tsam |
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30 # (the system sampling time) |
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31 # default: the default frequency range is selected as follows: (These |
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32 # steps are NOT performed if w is specified) |
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33 # (1) via routine bodquist, isolate all poles and zeros away from |
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34 # w=0 (jw=0 or exp(jwT)=1) and select the frequency |
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35 # range based on the breakpoint locations of the frequencies. |
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36 # (2) if sys is discrete time, the frequency range is limited |
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37 # to jwT in [0,2p*pi] |
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38 # (3) A "smoothing" routine is used to ensure that the plot phase does |
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39 # not change excessively from point to point and that singular |
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40 # points (e.g., crossovers from +/- 180) are accurately shown. |
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41 # outputs, inputs: the indices of the output(s) and input(s) to be used in |
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42 # the frequency response; see sysprune. |
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43 # outputs: |
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44 # mag, phase: the magnitude and phase of the frequency response |
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45 # G(jw) or G(exp(jwT)) at the selected frequency values. |
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46 # w: the vector of frequency values used |
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47 # If no output arguments are given, nichols plots the results to the screen. |
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48 # Descriptive labels are automatically placed. See xlabel, ylable, title, |
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49 # and replot. |
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50 # |
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51 # Note: if the requested plot is for an MIMO system, mag is set to |
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52 # ||G(jw)|| or ||G(exp(jwT))|| and phase information is not computed. |
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53 |
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54 # $Log$ |
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55 |
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56 # check number of input arguments given |
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57 if (nargin < 1 | nargin > 4) |
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58 usage("[mag,phase,w] = nichols(sys[,w,outputs,inputs])"); |
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59 endif |
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60 if(nargin < 2) |
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61 w = []; |
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62 endif |
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63 if(nargin < 3) |
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64 outputs = []; |
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65 endif |
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66 if(nargin < 4) |
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67 inputs = []; |
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68 endif |
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69 |
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70 [f, w] = bodquist(sys,w,outputs,inputs,"nichols"); |
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71 |
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72 [stname,inname,outname] = sysgetsignals(sys); |
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73 systsam = sysgettsam(sys); |
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74 |
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75 # Get the magnitude and phase of f. |
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76 mag = abs(f); |
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77 phase = arg(f)*180.0/pi; |
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78 |
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79 if (nargout < 1), |
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80 # Plot the information |
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81 if(gnuplot_has_multiplot) |
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82 oneplot(); |
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83 endif |
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84 gset autoscale; |
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85 if(gnuplot_has_multiplot) |
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86 gset nokey; |
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87 endif |
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88 clearplot(); |
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89 grid("on"); |
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90 gset data style lines; |
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91 if(is_digital(sys)) |
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92 tistr = "(exp(jwT)) "; |
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93 else |
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94 tistr = "(jw)"; |
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95 endif |
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96 xlabel("Phase (deg)"); |
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97 ylabel("Gain in dB"); |
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98 if(is_siso(sys)) |
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99 title(["Nichols plot of |[Y/U]",tistr,"|, u=", inname, ... |
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100 ", y=",outname]); |
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101 else |
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102 title([ "||Y(", tistr, ")/U(", tistr, ")||"]); |
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103 disp("MIMO plot from") |
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104 outlist(inname," "); |
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105 disp("to") |
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106 outlist(outname," "); |
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107 endif |
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108 md = 20*log10(mag); |
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109 axvec = axis2dlim([vec(phase),vec(md)]); |
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110 axis(axvec); |
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111 plot(phase,md); |
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112 mag = phase = w = []; |
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113 endif |
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114 endfunction |
