This is a simple problem which I'm having trouble finding an answer.(adsbygoogle = window.adsbygoogle || []).push({});

What would [tex] \sum_{n = 0}^{-1} 1[/tex] be?

Would this be undefined? 0? 2? or ???

The reason this came up in the first place is that I was trying to prove that the convolution sum is commutative, that is h*x = x*h.

I started with h*x

[tex] \sum_{n = - \infty}^{infty} h(n-m)x(m) [/tex]

making the substitution [itex]k = n-m [/itex], i get

[tex] \sum_{k = \infty}^{- \infty} x(k-m)h(k) [/tex]

The problem I have is witht the upper/lower limits of the sum. Does this mean the sum "decrements" through values of k?

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# Sum notation - lower/upper limits

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