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

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

  1. Luis

    Luis Guest

    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[5] + y[6] = x[5]
    5<6 so it's causal??

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

    Luis, Oct 29, 2004
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  2. Luis

    Ken Davis Guest

    Rewrite the system as:

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

    Does that clarify things?
    Ken Davis, Oct 30, 2004
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  3. Luis

    Abhay Kumar Guest

    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. 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
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