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How to Use Matlab's FFT Function for Discrete Fourier Transform?
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[QUOTE="wu_weidong, post: 1086770, member: 47160"] Hi, I am very new to Matlab, and I'm supposed to use the built-in FFT function to do discrete Fourier Transform for f(x) = sin x + 4 cos(5x) + (sin(6x))^2 on the interval [-pi, pi] with a uniform partition for the interval with n = 9. Then I have to (a) Plot the magnitudes of the Fourier coefficients and (b) Compute the first-order derivates at the grid points via FFT and compare them with f'(x). Here's what I have for part (a): x = -pi:0.25*pi:pi; y = sin(x)+4*cos(5*x) + sin(6*x).*sin(6*x); V=fft(y,9); plot(abs(V)); I'm a little confused with what the function fft returns. Does it return the Fourier coefficients of f(x) in my program? I got V = -0.0000 -5.9965 + 2.1842i -4.5019 - 4.8898i -8.3033 -15.3964i 0.8017 + 2.1116i 0.8017 - 2.1116i -8.3033 +15.3964i -4.5019 + 4.8898i -5.9965 - 2.1842i I also don't know how to find the first-order derivates at the grid points via FFT for part (b). What function do I use? Thank you very much! Regards, Rayne [/QUOTE]
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How to Use Matlab's FFT Function for Discrete Fourier Transform?
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