# Summation question and properties

• Apr 15th 2010, 10:17 AM
akhayoon
Summation question and properties
$\displaystyle y[n] = \sum_{m=-\infty}^{n} x[n]$.

I need to be able to solve this in order to figure some properties of the function

I actually have no clue what to do when I have negative infinity at the bottom.

I'd really like to know how to do this and these kinds of summations since my course on signals depends on knowing how to solve these.

anyways my idea would be somehow trying to get this summation to start from 0 instead of negative infinity
• Apr 15th 2010, 10:23 AM
AllanCuz
Quote:

Originally Posted by akhayoon
$\displaystyle y[n] = \sum_{m=-\infty}^{n} x[n]$.

I need to be able to solve this in order to figure some properties of the function

I actually have no clue what to do when I have negative infinity at the bottom.

I'd really like to know how to do this and these kinds of summations since my course on signals depends on knowing how to solve these.

anyways my idea would be somehow trying to get this summation to start from 0 instead of negative infinity

With respect to M what you have are 2 constants. So,

$\displaystyle \sum_{m=-\infty}^{n} x[n] = XN \sum_{m=-\infty}^{n} 1$

Unless you have a subscript M on your x that you didn't put in?