I did make an code of fast fourier transform. But there's an error on the code when I run it. There's anyone who more about and can assist or guide me to make the code running

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Mukendi Alonso
Mukendi Alonso 2024-3-14
评论： Walter Roberson 2024-3-15
I did make a code of FFT(fast fourier transform) using excel dataset (2049*7) as first column is taken as time and 2.3 and 4 as voltage A, B and C' and the 5,6 and 7 columns as currents A,B,C. When I run the code it give me error.
" Unrecognized function or variable 'Window_Nh'.
Error in fft_analyser(line 17)
Window_data = repmat(Window_Nh, 1, 7); % Replicate the window for 7 columns"
Below is half of the code that are note working
data = readtable('sadieldata.xlsx'); % load data
fs = 1000; % Sampling frequency
T = 1/fs; % Sampling period
N = 2049; % Number of samples
t = (0:N-1)*T; % Time Vector
U1 = data(:,1); % read phase 1 voltage
U2 = data(:,2); % read phase 2 voltage
U3 = data(:,3); % read phase 3 voltage
i1 = data(:,4); % read phase 1 current
i2 = data(:,5); % read phase 2 current
i3 = data(:,6); % read phase 3 current
%w = hann(N); % apply window function
Nh = 1:N; % number of windows for Hann Window
Nhr = rot90(Nh); % rotated window vector
data = rand(N, 7); % data of size N x 7; % Create a Hanniing window for each column
Window_Nhr = hann(N); % create a hanning window of length N
Window_data = repmat(Window_Nh, 1, 7); % Replicate the window for 7 columns
Window_rot = zeros(N, 7); % rotate Window vector to perform multiplication
for i = 1:size(Window_data, 2) % Iterate over columns
% Rotate the column by 90 degrees counterclockwise
Window_rot(:, i) = rot90(Window_data(:, i));
end

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采纳的回答

Walter Roberson
Walter Roberson 2024-3-14
You define a variable Window_Nhr but then you try to repmat Window_Nh
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Walter Roberson
Walter Roberson 2024-3-15
N = 2049; % Number of samples
That is a constant size
U1 = data(:,1); % read phase 1 voltage
That depends on the size of the input
Window_rot = zeros(N, 7); % rotate Window vector to perform multiplication
That is the constant size, by 7
U1_hann = U1.*Window_rot;
That attempts to multiply the variable-length data, by 2049 x 7 array. That will fail if the input data does not happen to be 2049 long.
Walter Roberson
Walter Roberson 2024-3-15
What you probably need to do is
U1 = data{:,1};
Overlap_size = 64; %NEEDS TO BE ADJUSTED
buffered_U1 = buffer(U1, N, Overlap_size);
Window_Nhr = hann(N);
hanned_U1 = Window_Nhr .* buffered_U1;

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