# Fourier analysis in matlab

Hi

I'm trying to use the fft function in matlab to compute the discrete fourier transform of a box signal. I'm told to assume that the signal x[n] is periodic with period N and the vector contains one period.

x[n]= box [n]

I'm am going to use these commands to make my vector

x=zeros(1,N)

x(N1,N2)=1

But I'm asked to justify my choise of N, N1 and N2

And I cant really figure out what values to pick for N, N1, N2.

If my vector is for example [ 0 0 0 0 1 1 1 0 0 0]
does that count as one period?

## Answers and Replies

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gneill
Mentor
Do you have a definition for "box signal"?

Do you know of any preferred conditions for the end points of the sample set? Do you know of any constraints placed on N (the number of sample points), by the fft function?

The box signal is just like a rectangle plotted with stem. i really dont have the formula but it just a vector with a few ones in it.

No i get to choose all my N,N1 and N2 values. But i have to justify why i choose them.
It's just to test the fft function

gneill
Mentor
The box signal is just like a rectangle plotted with stem. i really dont have the formula but it just a vector with a few ones in it.
So, no particular constraints on the ratio of 1's to 0's then?
No i get to choose all my N,N1 and N2 values. But i have to justify why i choose them.
It's just to test the fft function
This is why I asked about constraints. Look at the documentation for the fft function and see if you can spot any constraints mentioned there; you are not free to pick just any old value for N.