# How to complete the fourier Analysis using Matlab ?

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Hello !!

I have tried using the Matlab tutorial for FFT and DFT but I'm having extreme difficulty understanding the code and how I can use it in my question. My experience with matlab is only in data manipulation and plotting, so I'm struggling with the concepts.

So here is the question...

To compute the Cn coefficient given by

- Cn = 1/T * ∫ f(t)*e^(-2*pi*n*t/T) dt,

in which T is the period, and then Amplitude is

- sqrt(Re(Cn)^2 + Im(Cn)^2)
- F = n/T

then... how can I plot Amplitude vs Frequency using matlab functions. So far I have this function and req as mentioned above.

- f(t) = e^-t from -3 to 3
- T = 6
- F = -10:1:10

I would like to plot using matlab, but so far I'm doing integral manually and then just iterating values, and plotting them in matlab, can I use fft function or any other function to speed up the process ??

Many thanks

Megh

##### 1 Comment

dpb
on 11 Jan 2015

There's a complete example of computing/plotting the one-sided PSD at

doc fft

that should be pretty easy to follow what it's doing.

### Accepted Answer

Rick Rosson
on 11 Jan 2015

Edited: Rick Rosson
on 11 Jan 2015

doc fft

doc fftshift

doc abs

doc angle

doc plot

doc stem

doc xlabel

doc ylabel

doc grid

doc xlim

doc ylim

### More Answers (2)

Youssef Khmou
on 11 Jan 2015

Try to study and alter this example :

Fs=10;

t=-3:1/Fs:3;

x=exp(-t);

plot(t,x)

N=1000; % N points for frequency computation

fx=fftshift(fft(x,N))/sqrt(N);

fx=fx.*conj(fx);

% frequency axis

f=(-N/2:N/2-1)*Fs/(2*N);

figure; plot(f,fx);

Megh
on 13 Jan 2015

Edited: Megh
on 13 Jan 2015

##### 1 Comment

Katherine Zheng
on 18 Mar 2022

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