# z transforms

Discussion in 'Homework Help' started by silvrstring, Aug 11, 2008.

1. ### silvrstring Thread Starter Active Member

Mar 27, 2008
159
0
Hey-lo everybody,

I am having trouble finding information on solving difference equations with the "iteration method."

The Q: was solve the following difference equation

y(k+2) + y(k+1) + yk = 0 where y0 = 0, and y1 = 1

I got y0=0, y1=1, y2=-1, y3=0, y4=1, y5=-1, y6=0 ...
or {0,1,-1,0,1,-1,0,...}

I don't know what to do from here, and my text has nothing on the "Iteration method." I've searched the net, and the search results were either books I had to pay for, articles I had to pay for, or simply much more info than I need.

If anyone can tell me where I go from here, I would appreciate it. I'll be taking signal processing next semester, and I would like to get this stuff "down pat" before then.

Thanks,
silvrstring

P.S. Yes, this is homework. But I will be happy if you can just give an example.

2. ### Ratch New Member

Mar 20, 2007
1,068
4
silvrstring,

You already did it. You must have gotten the sequence as far as you did by adding the last two numbers and subtracting from 0 to get the next number in the sequence. So you keep doing that until you get the next number, and the next number, and the next number, and the next number, ... . That is an iteration, get it?

The only thing left to do is to figure out a formula for the each number in the sequence. Like maybe y(k) = mod(k/3)-1 for k=1 to infinity. There may be other formulas you can dream up.

Ratch

3. ### silvrstring Thread Starter Active Member

Mar 27, 2008
159
0
Oh, I see. Thanks Ratch. I got it.