Discrete-Time Functions

Discussion in 'Math' started by RdAdr, Oct 6, 2015.

  1. RdAdr

    Thread Starter Member

    May 19, 2013
    214
    1
    I attached a picture with my confusion.
    Hopefully, someone will be able to shed some light upon this.
     
  2. WBahn

    Moderator

    Mar 31, 2012
    17,788
    4,808
    When you claim

    f(u[n] - u[n-4]) = f(u[n]) - f(u[n-4])

    you are claiming that f() is a linear function.

    Is it?

    Why are you saying that

    f(u[n-4]) = (n-4)u[n-4]

    You have

    f(x[n]) = n * x[n]

    Whatever you plug in as the argument of f(), that only replaces the parameter x[n] in the expression.
     
  3. Lool

    Member

    May 8, 2013
    117
    12
    Just a quick comment that the step f(u[n-4])=(n-1) u[n-4] is the incorrect step as mentioned above.

    The step f(u[n] - u[n-4]) = f(u[n]) - f(u[n-4]) is correct because this is a linear time varying system.
     
  4. RdAdr

    Thread Starter Member

    May 19, 2013
    214
    1
    I figured it out. I was confused between the actual model and the input-output relationship that arises from it.
    Thanks for the answers.
     
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