Question
I tried to run the following commands in the example of the PMTM documentation: randn('state',0); fs = 1000; t = 0:1/fs:0.3; x = cos(2*pi*t*200) + 0.1*randn(size(t)); [Pxx,Pxxc,f] = pmtm(x,3.5,512,fs,0.99); hpsd = dspdata.psd([Pxx Pxxc],{f,fs}) plot(hpsd) I received the following errors: ??? Error using ==> dspdata.abstractfreqresp.initialize The number of frequency points must equal the length of the data.
Expert Answer
Prashant Kumar
PhD Expert
Answered Aug 25, 2026
This bug has been fixed in Release 14 Service Pack 2 (R14SP2). For previous releases, please read below for any possible workarounds:
We have verified that the example in the PMTM function documentation is incorrect in Signal Processing Toolbox 6.2 (R14).
To work around this issue, please use the following code instead:
randn('state',0);
fs = 1000;
t = 0:1/fs:0.3;
x = cos(2*pi*t*200) + 0.1*randn(size(t));
[Pxx,Pxxc,f] = pmtm(x,3.5,512,fs,0.99);
hpsd = dspdata.psd([Pxx Pxxc],'Fs',fs); % <----- the corrected line
plot(hpsd)
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