# How to computer a frequency spectrum and find its largest spectral energy

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PetronasAMG on 24 Sep 2021
Edited: PetronasAMG on 26 Sep 2021
I am given set of equation
I am suppose to plot x1 x2 and x3 as a 3d dimensional phase, but direction wants me to omit any possible initial transient trajectory.

Chunru on 24 Sep 2021
Edited: Chunru on 24 Sep 2021
fs = 10;
tspan = [0:1/fs:100]; % specify the time points
xint = [3.0;2.0;1.0];
[t,x]= ode45(@nonlin,tspan,xint);
% remove some trainsition part of x
t = t(100:end);
x = x(100:end, :);
subplot(211); plot(t, x)
subplot(212); plot(20*log10(abs(fft(x))))
function dxdt = nonlin(t,x)
e = 2.5;
dxdt = zeros(3,1);
dxdt(1) = -(x(2)+x(3));
dxdt(2) = x(1) + ((1/5)*x(2));
dxdt(3) = (1/5)+(((x(1)-e))*x(3));
end
##### 2 CommentsShow 1 older commentHide 1 older comment
Chunru on 24 Sep 2021
In the original code above, I did not remove the transition part. Just kept them. I update the code to remove the transistion period.

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