plot the fundamental harmonic wave
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Hello everyone. I have exported data to an Excel spreadsheet where the x-axis is represented by theta (in radians). How can I plot the fundamental harmonic wave from this wave data?
6 个评论
Mathieu NOE
2023-11-20
hello
you can work either in time / angular domain , by applying a band pass filter centered at your target frequency (fundamental)
or you can work in the frequency domain (fft your data, then keep only the frequency(ies) of interest and do ifft)
hamid k
2023-11-20
Mathieu NOE
2023-11-21
well, show me your data (and code) and I will answer you
Star Strider
2023-11-21
The fft function only wants ‘theta’ to be sampled at a constant interval. It does not know or care what ‘theta’ actually is (seconds, years, metres, parsecs, radians, degrees, or anything else). The frequency unit will then be the inverse of that (cycles/second, cycles/metre, cycles/parsec, cycles/radian, cycles/degree).
hamid k
2023-11-23
Mathieu NOE
2023-11-23
see my answer below
采纳的回答
Mathieu NOE
2023-11-23
hello again
so this is it, we do a single frequency DFT (aka order extraction) at the second harmonic (as we have two period of signal for theta ranging from 0 to 2*pi
result :
code :
%Load Excel file
data = readmatrix('Book1.xlsx'); % theta(Rad) Br(T)
%Extract theta and y columns
theta = data(:,1); % theta (0 - 2pi)
y = data(:,2); % y data
%%%%%%%%%%%%% main code %%%%%%%%%%%%%%%%%
% 2nd order extraction (DFT)
order = 2;
% model fit : X = A*cos(order*theta) + B*sin(order*theta) + C
C = mean(y);
y = y-C;
n = numel(theta);
A = 2/n*trapz(y.*cos(order*theta));
B = 2/n*trapz(y.*sin(order*theta));
yfit = A*cos(order*theta) + B*sin(order*theta) + C;
% plot
figure(1),
plot(theta, y, 'b',theta, yfit, 'r')
legend('data','model fit');
1 个评论
Abdullah
2024-4-24
Hello Mathieu,
i tried to use your code with my data, but it does not work, do you have an idea?
https://de.mathworks.com/matlabcentral/answers/2110271-how-to-plot-the-fundamental-harmonic-wave-from-given-data?s_tid=srchtitle
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Sulaymon Eshkabilov
2023-11-20
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