Express this sequence as a unit step function (discrete)

• January 1st 2011, 11:02 PM
TechnicianEngineer
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
$x(n) = -\sigma(n+1)-\sigma(n+2)-\sigma(n+3)-\sigma(n+4)?$

b. unit step function

x(n) = -u(-(n+5))-u(-n)?
• January 2nd 2011, 09:01 PM
snowtea
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)
• January 3rd 2011, 02:31 AM
TechnicianEngineer
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
• January 3rd 2011, 05:31 AM
snowtea
Yes, you are absolutely right on that. Silly me :)

But I'm glad you got the concept.