Identification of Resonance frequencies
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I want to evaluate Resonanat frequencies and Magnitude of FRF from FRF vs Frequency Plot.I have used the following steps but the answer is incorrect.Pl help me to locate the mistake a = [30000 x 1 readings]; ffa = fft(a); F =[30000 x 1 readings]; fff = fft(F); H = ffa./fff; aH = abs(H); L = 30000; NFFT = 32768; Fs = 10000; y = aH; Y = fft(y,NFFT)/L; f = Fs/2*linspace(0,1,NFFT/2+1); semilogy(f,aH) After the execution the statement is shown as ??? Error using ==> semilogy Vectors must be the same lengths.** Pl tell me length of which vector is not matching SLG
2 Comments
Andrew Newell
on 6 Jul 2011
Please format your code (see http://www.mathworks.com/matlabcentral/answers/7885-tutorial-how-to-format-your-question).
Paulo Silva
on 6 Jul 2011
Just look at your workspace window and the Size tab that tells you the sizes of all the current workspace variables, you can also do size(f) and size(aH) to know their sizes.
Answers (1)
Rick Rosson
on 6 Jul 2011
The problem is that the array f is of size 1 x 16385, whereas the array aH is of size 30000 x 1. When you call semilogy(f,aH), MATLAB expects that f and aH will have the same size and shape. Since they do not, you are getting the error messaage.
Please help us help you:
1. Reformat your code as suggested in Andrew Newell's comment.
2. What size is the variable y in your code?
Thanks!
Rick
2 Comments
Rick Rosson
on 11 Jul 2011
I do not understand what you are trying to do, what is not working right now, or what your question is.
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