Hi everyone,

I am trying to extract the correct phase angle from a forced damped harmonic oscillator using matlab ode45() function to solve it and then using matlab fft to do fft analysis and try to extract the phase angle from the fft. Code:

`tspan=[0,50];init=[-2;0];step=1;% call the solver`

[t1,y1]=ode45(@f1,tspan,init);%Find FFT

m = length(y1) % Window length

Y1=fft(y1(:,1),m);n = fix(m);plot(t1(1:n,1),y1(1:n,1),t1(1:n,1),ifft(Y1),'*')%Find the phase angle

FT_power2 = abs(Y1).^2;FT_phase2= (((angle(Y1))) * 180/pi);[c2,i2] = max(FT_power2);phase = FT_phase2(i2)

Problem is I do not think I am getting the correct angle (or I am completely not understanding what I am suppose to get). The function in question being solved by ode45 is:

`yprime = -c*y(2)-k*y(1)+4*sin(2*t); where c,k,y(1) and y(2) are known.`

Shouldn't I get angle of 45 (since it would 0 + the pi/2 lag from the sin function)? I am getting:

178.7608 in degrees.

Please help me out if possible I am at complete loss.

PS:I am completely new to fft and such.

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