Documentation of nyqplot

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Function Synopsis

nyqplot(G,sd,mode)

Help text

NYQPLOT  plots the Nyquist diagram of a frequency function.
   NYQPLOT(G)  or  NYQPLOT(G,SD)

   G is entered as the transfer function(s) of the standard frequency
   function format, produced by TH2FF, SPA or ETFE.
   See also FREQFUNC.

   Several plots in the same diagram are obtained by
   NYQPLOT([G1 G2 .. Gn])
   The transfer functions Gk need not be given at the same frequencies.
   If SD is specified to a number larger than zero, also confidence
   intervals for the functions (corresponding to SD standard deviations)
   are shown as dash-dotted  curves.

   The default mode is that ENTER will advance the plot from one
   input to the next (if any). To obtain all plots in the same diagram
   use nyqplot(G,SD,'same').
   Frequency functions for different outputs will always be given in
   separate plots.
   See also BODEPLOT, and FFPLOT.

Cross-Reference Information

Listing of function nyqplot

function nyqplot(G,sd,mode)

%   L. Ljung 10-7-89
%   Copyright (c) 1986-98 by The MathWorks, Inc.
%   $Revision: 2.4 $  $Date: 1997/12/02 03:43:37 $

if nargin<1
     disp('Usage: NYQPLOT(G)')
     disp('       NYQPLOT(G,SD,C,MODE)')
     return
end

if (nargin==1), sd=0; mode='sep';end
if (nargin==2),mode='sep';end
newplot;
mode=mode(1:3);

[m,n]=size(G);
inputs1=G(1,:);mo=fix(inputs1/1000);mmo=max(mo);
kko=[]; % The output indices
for k=[0:mmo],if length(find(mo==k))>0,kko=[kko k];end,end
G=G(2:m,:);
for ko=kko+1
inputs=inputs1-(ko-1)*1000;
mi=max(inputs(find(inputs<19)));

kki=[]; % The input indices
for k=[1:mi 0], if length(find(inputs==k))>0,kki=[kki k];end,end

if mode=='sep'
for k=kki
if k~=0,
clf

        gp=G(:,find(inputs==20+k))*pi/180;
        polar(gp,G(:,find(inputs==k)))
        ax=axis; hold on, polar([0 0],ax(1:2)),
        polar([pi pi]/2,ax(1:2)),hold off
        if sd>0,hold on,
        ind=find(k+50==inputs);
        polar(gp,G(:,ind-1)+sd*G(:,ind),'-.')
        polar(gp, G(:,ind-1)-sd*G(:,ind),'-.')
        hold off,end



        title(['NYQUIST PLOT, input # ',int2str(k),' output # ',int2str(ko)])

else disp('No Nyquist plot for spectra!'),end


if k~=kki(length(kki)),pause,end
end
end

if mode=='sam'
                gp=G(:,find(inputs<39 & inputs > 19))*pi/180;
        polar(gp,G(:,find(inputs<20)))
        ax=axis; hold on, polar([0 0],ax(1:2)),
        polar([pi pi]/2,ax(1:2)),hold off
        if sd>0,hold on,
        ind=find(inputs<69 & inputs>49);
        polar(gp,G(:,ind-1)+sd*G(:,ind),'-.')
        polar(gp, G(:,ind-1)-sd*G(:,ind),'-.')

        hold off,end

        title(['NYQUIST PLOT output # ',int2str(ko)])
      end
if ko~=kko(length(kko))+1,pause,end
end
hold off
set(gcf,'NextPlot','replace');