Nyquist function returns error

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Daniel Zwart
Daniel Zwart 2011-6-13
I get an error when trying to use the nyquist function, either with or without an argument. The error stems from a 'switch' argument having a double as an input. I have Matlab r2010a student edition with control system toolbox version 8.5 running on a 64-bit Dell Latitude E6510 with Windows 7. Please let me know if more information would be useful. The error is as follows:
num=[1 2];
den=[1 -2 -3];
h=tf(num,den)
nyquist(h)
??? SWITCH expression must be a scalar or string constant.
Error in ==> cot at 30
switch varargin{arg}
Error in ==> freqgrid>LocalResGrid at 244
ct = -cot(angles);
Error in ==> freqgrid at 102
[wnew,dlnew,drnew] = LocalResGrid(zp(:),Ts,dnpts,Grade);
Error in ==> ltidata.freqresp at 46
w = freqgrid(z,p,Ts,Grade,Focus);
Error in ==> resppack.ltisource.nyquist at 24
[mag,phase,w,FocusInfo] = freqresp(SysData(ct),1,wspec,true);
Error in ==> wavepack.waveform.draw at 21
feval(this.DataFcn{:});
Error in ==> wrfc.plot.draw at 18
draw(wf)
Error in ==> wrfc.plot.init_listeners>LocalRefreshPlot at 119
draw(this)
Warning: Error occurred while evaluating listener callback.
> In lti.nyquistplot at 103
In lti.nyquist at 83
In exresp at 40
In nyquist at 67

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采纳的回答

Walter Roberson
Walter Roberson 2011-6-13
The built-in cot() function does not have 30 lines or any switch statement.
Please use
which -all cot
to see if perhaps you have accidentally introduced your own cot.m that is overriding the MATLAB one.

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