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Math Help - Express this sequence as a unit step function (discrete)

  1. #1
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    Express this sequence as a unit step function (discrete)

    express the sequence {0,...,0,-1,-1,-1,-1,0(origin),0,0,0...,0} in terms of
    a. scaled/shifted impulses
    is the answer
    x(n) = -\sigma(n+1)-\sigma(n+2)-\sigma(n+3)-\sigma(n+4)?


    b. unit step function
    is the answer

    x(n) = -u(-(n+5))-u(-n)?
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  2. #2
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    For (a), I believe you are correct.

    For (b), consider the simple sequence y ...,0,0(origin),1,1,1,1,0,0,...
    y(n) = u(n) - u(n-5)

    Now x(n) = -y(-n) = -u(-n) + u(-n-5)
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  3. #3
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    no you are wrong on
    (b) it's suppossed to be {0,0,0(origin),1,1,1,1,0,0} ==> y(n) = u(n-1)-u(n-5)

    Now -y(-n) = -u(-n-1)) + u(-n-5))

    clarify me pls
    Last edited by TechnicianEngineer; January 3rd 2011 at 04:23 AM.
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  4. #4
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    Yes, you are absolutely right on that. Silly me

    But I'm glad you got the concept.
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