# Need help with Fourier Transform fft

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Mackenzie Weeks on 24 May 2021
Commented: Mackenzie Weeks on 24 May 2021
clc;clear all
X = [8 9 9 6 10 2 5 6];
Y = fft(X)
Hi,
Im given an index (j) (0,1,2,3,4,5,6,7), data recorded(8,9,9,6,10,3,5,6), and DFT values (7, 0.28-1.03 i,0.5,-0.78-0.03 i,1,-0.78+.03 i,0.5,0.28+1.03i). I am supposed to test my FFT algorithm to recreate the discrete Fourier transform of this data set along with recreating the discrete fourier transform by writing a program that computes the discrete fourier transform. This is what i have so far, but its giving me the wrong DFT values
Y =
Columns 1 through 6
55.0000 + 0.0000i 2.9497 - 8.9497i 4.0000 + 1.0000i -6.9497 - 0.9497i 9.0000 + 0.0000i -6.9497 + 0.9497i
Columns 7 through 8
4.0000 - 1.0000i 2.9497 + 8.9497i
Any ideas of how to start?
Paul on 24 May 2021
Are you sure about the problem statement? The data and the DFT values don't seem to be consistent with each other:
fft([8 9 9 6 10 3 5 6])
ans =
56.0000 + 0.0000i 2.2426 - 8.2426i 4.0000 + 0.0000i -6.2426 - 0.2426i 8.0000 + 0.0000i -6.2426 + 0.2426i 4.0000 + 0.0000i 2.2426 + 8.2426i
Mackenzie Weeks on 24 May 2021
i accidentally typed 2 instead of 3, but even when thats chnaged its not outputting the DFT values that I'm supposed to be getting (7, 0.28-1.03 i,0.5,-0.78-0.03 i,1,-0.78+.03 i,0.5,0.28+1.03i)

Girijashankar Sahoo on 24 May 2021
MATLAB code DFT output is correct. You can varify it by first DFT value which is sum of data sequence
55=sum([8 9 9 6 10 2 5 6])
Mackenzie Weeks on 24 May 2021
oh okay i see what i did wrong! I didn't normalize my data. Once i did, I got the correct DFT values. Thanks :)