# conv function to compute h[n]

Discussion in 'Programmer's Corner' started by angelita, Nov 30, 2010.

1. ### angelita Thread Starter Member

May 29, 2009
25
0
using conv function
find : h[n] for the following

y[n+2]-4y[n+1]+4y[n]=2x[n+2]-2x[n+1]

Dec 5, 2009
5,201
315
You first.

3. ### angelita Thread Starter Member

May 29, 2009
25
0
i asked for help bcoz i have no idea how to solve it

4. ### retched AAC Fanatic!

Dec 5, 2009
5,201
315
Oh, Im sorry, I didn't see where you asked for help.

It looked like you just told us to solve it.

Is this a homework problem?

What do you know so far about it?

5. ### angelita Thread Starter Member

May 29, 2009
25
0
i used the conv function with values of h and x to find the convolution

but i dont know how to de the reverse

6. ### steveb Senior Member

Jul 3, 2008
2,433
469
Have you learned about z-transforms yet? This problem is straightforward in the frequency domain. If you have been taught z-transforms, we can guide you through the process which begins by taking the z-transform of your difference equation and then solving for H(z)=Y(z)/X(z). Then you take the inverse z-transform (using partial fraction expansion and a transform table) to work back to the impulse response funtion h[n].

It's a little trickier to work it out in the discrete time domain because the system is unstable and the impulse response continues to increase to infinity. Hence, you need to work out a recursion equation to get a closed form. This can also be done, but I only recommend this approach if you haven't been taught z-transforms yet.

Last edited: Nov 30, 2010