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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, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
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18 ## 02110-1301 USA. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {[@var{realp}, @var{imagp}, @var{w}] =} nyquist (@var{sys}, @var{w}, @var{out_idx}, @var{in_idx}, @var{atol}) |
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22 ## @deftypefnx {Function File} {} nyquist (@var{sys}, @var{w}, @var{out_idx}, @var{in_idx}, @var{atol}) |
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23 ## Produce Nyquist plots of a system; if no output arguments are given, Nyquist |
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24 ## plot is printed to the screen. |
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25 ## |
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26 ## Compute the frequency response of a system. |
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27 ## |
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28 ## @strong{Inputs} (pass as empty to get default values) |
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29 ## @table @var |
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30 ## @item sys |
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31 ## system data structure (must be either purely continuous or discrete; |
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32 ## see @code{is_digital}) |
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33 ## @item w |
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34 ## frequency values for evaluation. |
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35 ## If sys is continuous, then bode evaluates @math{G(@var{jw})}; |
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36 ## if sys is discrete, then bode evaluates @math{G(exp(@var{jwT}))}, |
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37 ## where @var{T} is the system sampling time. |
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38 ## @item default |
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39 ## the default frequency range is selected as follows: (These |
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40 ## steps are @strong{not} performed if @var{w} is specified) |
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41 ## @enumerate |
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42 ## @item via routine @command{__bodquist__}, isolate all poles and zeros away from |
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43 ## @var{w}=0 (@var{jw}=0 or @math{exp(@var{jwT})=1}) and select the frequency |
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44 ## range based on the breakpoint locations of the frequencies. |
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45 ## @item if @var{sys} is discrete time, the frequency range is limited |
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46 ## to @var{jwT} in |
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47 ## @ifinfo |
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48 ## [0,2p*pi] |
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49 ## @end ifinfo |
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50 ## @iftex |
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51 ## @tex |
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52 ## $ [ 0,2 p \pi ] $ |
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53 ## @end tex |
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54 ## @end iftex |
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55 ## @item A ``smoothing'' routine is used to ensure that the plot phase does |
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56 ## not change excessively from point to point and that singular |
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57 ## points (e.g., crossovers from +/- 180) are accurately shown. |
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58 ## @end enumerate |
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59 ## @item atol |
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60 ## for interactive nyquist plots: atol is a change-in-slope tolerance |
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61 ## for the of asymptotes (default = 0; 1e-2 is a good choice). This allows |
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62 ## the user to ``zoom in'' on portions of the Nyquist plot too small to be |
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63 ## seen with large asymptotes. |
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64 ## @end table |
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65 ## @strong{Outputs} |
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66 ## @table @var |
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67 ## @item realp |
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68 ## @itemx imagp |
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69 ## the real and imaginary parts of the frequency response |
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70 ## @math{G(jw)} or @math{G(exp(jwT))} at the selected frequency values. |
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71 ## @item w |
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72 ## the vector of frequency values used |
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73 ## @end table |
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74 ## |
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75 ## If no output arguments are given, nyquist plots the results to the screen. |
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76 ## If @var{atol} != 0 and asymptotes are detected then the user is asked |
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77 ## interactively if they wish to zoom in (remove asymptotes) |
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78 ## Descriptive labels are automatically placed. |
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79 ## |
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80 ## Note: if the requested plot is for an @acronym{MIMO} system, a warning message is |
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81 ## presented; the returned information is of the magnitude |
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82 ## @iftex |
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83 ## @tex |
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84 ## $ \Vert G(jw) \Vert $ or $ \Vert G( {\rm exp}(jwT) \Vert $ |
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85 ## @end tex |
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86 ## @end iftex |
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87 ## @ifinfo |
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88 ## ||G(jw)|| or ||G(exp(jwT))|| |
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89 ## @end ifinfo |
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90 ## only; phase information is not computed. |
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91 ## @end deftypefn |
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92 |
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93 ## Author: R. Bruce Tenison <btenison@eng.auburn.edu> |
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94 ## Created: July 13, 1994 |
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95 ## A. S. Hodel July 1995 (adaptive frequency spacing, |
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96 ## remove acura parameter, etc.) |
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97 ## Revised by John Ingram July 1996 for system format |
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98 |
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99 function [realp, imagp, w] = nyquist (sys, w, outputs, inputs, atol) |
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100 |
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101 ## Both bode and nyquist share the same introduction, so the common |
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102 ## parts are in a file called __bodquist__.m. It contains the part that |
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103 ## finds the number of arguments, determines whether or not the system |
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104 ## is SISO, andd computes the frequency response. Only the way the |
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105 ## response is plotted is different between the two functions. |
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106 |
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107 ## check number of input arguments given |
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108 if (nargin < 1 || nargin > 5) |
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109 print_usage (); |
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110 endif |
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111 if (nargin < 2) |
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112 w = []; |
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113 endif |
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114 if (nargin < 3) |
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115 outputs = []; |
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116 endif |
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117 if (nargin < 4) |
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118 inputs = []; |
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119 endif |
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120 if (nargin < 5) |
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121 atol = 0; |
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122 elseif (! (is_sample (atol) || atol == 0)) |
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123 error ("nyquist: atol must be a nonnegative scalar") |
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124 endif |
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125 |
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126 ## signal to __bodquist__ who's calling |
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127 |
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128 [f, w, sys] = __bodquist__ (sys, w, outputs, inputs, "nyquist"); |
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129 |
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130 ## Get the real and imaginary part of f. |
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131 realp = real (f); |
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132 imagp = imag (f); |
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133 |
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134 ## No output arguments, then display plot, otherwise return data. |
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135 if (nargout == 0) |
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136 dnplot = 0; |
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137 while (! dnplot) |
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138 plot (realp, imagp, "- ;+w;", realp, -imagp, "-@ ;-w;"); |
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139 |
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140 grid ("on"); |
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141 |
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142 if (is_digital (sys)) |
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143 tstr = " G(e^{jw}) "; |
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144 else |
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145 tstr = " G(jw) "; |
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146 endif |
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147 xlabel (sprintf ("Re(%s)", tstr)); |
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148 ylabel (sprintf ("Im(%s)", tstr)); |
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149 |
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150 [stn, inn, outn] = sysgetsignals (sys); |
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151 if (is_siso (sys)) |
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152 title (sprintf ("Nyquist plot from %s to %s, w (rad/s) in [%e, %e]", |
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153 inn{1}, outn{1}, w(1), w(end))); |
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154 endif |
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155 |
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156 axis (axis2dlim ([[realp(:), imagp(:)]; [realp(:), -imagp(:)]])); |
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157 |
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158 ## check for interactive plots |
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159 dnplot = 1; # assume done; will change later if atol is satisfied |
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160 if (atol > 0 && length (f) > 2) |
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161 |
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162 ## check for asymptotes |
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163 fmax = max (abs (f)); |
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164 fi = find (abs (f) == fmax, 1, "last"); |
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165 |
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166 ## compute angles from point to point |
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167 df = diff (f); |
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168 th = atan2 (real (df), imag (df)) * 180 / pi; |
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169 |
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170 ## get angle at fmax |
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171 if (fi == length(f)) |
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172 fi = fi-1; |
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173 endif |
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174 thm = th(fi); |
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175 |
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176 ## now locate consecutive angles within atol of thm |
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177 ith_same = find (abs (th - thm) < atol); |
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178 ichk = union (fi, find (diff (ith_same) == 1)); |
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179 |
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180 ## locate max, min consecutive indices in ichk |
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181 loval = max (complement (ichk, 1:fi)); |
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182 if (isempty (loval)) |
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183 loval = fi; |
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184 else |
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185 loval = loval + 1; |
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186 endif |
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187 |
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188 hival = min (complement (ichk, fi:length(th))); |
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189 if (isempty (hival)) |
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190 hival = fi+1; |
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191 endif |
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192 |
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193 keep_idx = complement (loval:hival, 1:length(w)); |
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194 |
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195 if (length (keep_idx)) |
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196 resp = input ("Remove asymptotes and zoom in (y or n): ", 1); |
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197 if (resp(1) == "y") |
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198 dnplot = 0; # plot again |
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199 w = w(keep_idx); |
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200 f = f(keep_idx); |
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201 realp = real (f); |
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202 imagp = imag (f); |
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203 endif |
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204 endif |
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205 |
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206 endif |
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207 endwhile |
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208 w = realp = imagp = []; |
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209 endif |
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210 |
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211 endfunction |
