Finding an integer with matlab fft function

1. Apr 7, 2008

ser23

Hi, I hope someone could help me, I have been trying to solve this problem with FFT in matlab, why?, because my teacher gave it as homework. The problem is the following.

Obtain the value of the following integer using FFT:

the integer goes from [-infinte, infinite], and the function is x^2*exp(-x^2)*dx

He told us to check the definition of the fourier transform and I checked in books, matlab everywhere and I cant find any info that could help me, I hope someone here can, THANK YOU.

2. Apr 7, 2008

chroot

Staff Emeritus
I have no idea what you mean by "obtain the value of the following integer."

Can you please post the problem exactly as it was given to you?

- Warren

3. Apr 7, 2008

ser23

Sure, and thanks for your help

Solve the following integer using the FFT in MATLAB:

integer goes from[-infinite, infinite] and the function is:
x^2*exp(-x^2)dx

TIP: Check the fourier transform definition. (the tip is from my teacher).

By the way I tried to translate the problem the best I can, because even in spanish what my teacher writes is difficult to understand or to find the answer he is looking for by the problem he gave us.

4. Apr 7, 2008

Dr Transport

is he asking for the integral??????

5. Apr 8, 2008

diiid

Yes, It should be intergral because of the dx at the end of the fuction.

6. Apr 8, 2008

ser23

hi, yes the integral im sorry.

7. Apr 9, 2008

qspeechc

He's asking how you would write a program to find the integral using the Fast Fourier Transform (FFT). I don't know how to do it, but I thought I should clear that up for other people.

8. Apr 9, 2008

chroot

Staff Emeritus
Seems like you should be able to evaluate this integral by using integration by parts. I don't understand what MATLAB has to do with it.

- Warren

9. Apr 9, 2008

ser23

Actually this is the solution my teacher gave us. He said that this is a cool way to calculate an integral, I still don't get it, hope this info helps someone, and thank you all foru your help and good intentions.

>> N=1000;
x=linspace(-10,10,N);
dx=x(2)-x(1);
y=x.^2.*exp(-x.^2);
plot(x,y);
sum( y)*dx;
mm=(fft( y));
mm(1)*dx;
>>