# plotting FFT in matlab

Started by August 12, 2008
```suppose f(x)=exp(-x^2) then it's fourier transform is also
exponential. I'm trying to perform FFT and plot it. I'm using this but
it is not showing exponential behavior. please help  me with plotting
the FFT

x=-10:0.01:10;
y=exp(-x.^2);
N=5000;
z=fft(y,N);
F=[-N/2:N/2-1]/N;
plot(F,z,'b');
```
```>suppose f(x)=exp(-x^2) then it's fourier transform is also
>exponential. I'm trying to perform FFT and plot it. I'm using this but
>it is not showing exponential behavior. please help  me with plotting
>the FFT
>
>x=-10:0.01:10;
>y=exp(-x.^2);
>N=5000;
>z=fft(y,N);
>F=[-N/2:N/2-1]/N;
>plot(F,z,'b');
>
First of all, your z is complex, so using a simple plot command is going
to give you a warning (I have 2008b, I don't remember how older MATLAB
behaves).  Next, to get the "standard" view, with 0 Hz in the middle, you
should apply an fftshift to whatever component you want to view, e.g.,
plot(F, real(fftshift(z)), 'b').  If you plot the absolute value of z
(abs(fftshift(z))), you'll get a similar exponential shape, btw.

Mark
```
```On Aug 12, 11:46&#2013266080;am, novis <stands...@gmail.com> wrote:
> suppose f(x)=exp(-x^2) then it's fourier transform is also
> exponential. I'm trying to perform FFT and plot it. I'm using this but
> it is not showing exponential behavior. please help &#2013266080;me with plotting
> the FFT
>
> x=-10:0.01:10;
> y=exp(-x.^2);
> N=5000;
> z=fft(y,N);
> F=[-N/2:N/2-1]/N;
> plot(F,z,'b');

Gaussian.
```
```>(I have 2008b, I don't remember how older MATLAB behaves).
That would be 2008a, not b.

Mark
```
```On Tue, 12 Aug 2008 08:46:37 -0700 (PDT), novis <standshik@gmail.com>
wrote:

>suppose f(x)=exp(-x^2) then it's fourier transform is also
>exponential. I'm trying to perform FFT and plot it. I'm using this but
>it is not showing exponential behavior. please help  me with plotting
>the FFT
>
>x=-10:0.01:10;
>y=exp(-x.^2);
>N=5000;
>z=fft(y,N);
>F=[-N/2:N/2-1]/N;
>plot(F,z,'b');

Hi novis,
Try the following:

clear, clc
x = -3:0.1:3;
y = exp(-x.^2);

figure(1)
subplot(3,1,1)
plot(x, real(y), '-bo', 'markersize', 2)
subplot(3,1,2)
plot(x, imag(y), '-bo', 'markersize', 2)

N = 1024;
z = fft(y,N);
Mag = abs(z);
Mag_shifted = fftshift(Mag);
F = [-N/2:N/2-1]/N;
subplot(3,1,3)
plot(F, Mag_shifted, 'b');

[-Rick-]

```