plot the fundamental harmonic wave

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hamid k 2023-11-19

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评论： Abdullah 2024-4-24

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?

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hamid k 2023-11-23

Data and code.zip

You can find the attached data and code files here.

Mathieu NOE 2023-11-23

see my answer below

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Mathieu NOE 2023-11-23

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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');