# Is this system causal? (I think it is but I need to make sure...)

Discussion in 'MATLAB' started by Luis, Oct 29, 2004.

1. ### LuisGuest

x[n] --> [system] -->y[n]
input output

System: y[n] + y[n+1] = x[n]

A system is causal if for every choice of n0, the output sequence
(y[n]) value at the index n=n0, depends only on the input sequence
(x[n]) values for n<=n0

so let n0=5
y + y = x
5<6 so it's causal??

I think it's causal, but I just want to corroborate. Any help is
appreciated. Thanks

Luis

Luis, Oct 29, 2004

2. ### Ken DavisGuest

Rewrite the system as:

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

Does that clarify things?

Ken Davis, Oct 30, 2004

3. ### Abhay KumarGuest

also rewrite as
y[n]+y[n-1]=x[n-1] % delay operator form. Its more clear here.

The order of input should be equal to or less than order of output
for system to be causal-----> rule of thumb.

A. Kumar

Abhay Kumar, Oct 30, 2004
4. ### Leendert CombeeGuest

Has nothing to do with Matlab, but is just discrete signal
processing. Don't want to discourage you but I think you need to go
back to your textbooks and learn about causility. This example is so
trivial that if you only _think_ it is causal instead of knowing it
for sure you haven't understood the concept yet.

Leendert Combee, Oct 30, 2004