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Simplifying Finite Sums With A Variable # of Terms
*To*: mathgroup at smc.vnet.net
*Subject*: [mg21744] Simplifying Finite Sums With A Variable # of Terms
*From*: Wretch <arc at astro.columbia.edu>
*Date*: Wed, 26 Jan 2000 03:45:43 -0500 (EST)
*Organization*: Vacuum
*Sender*: owner-wri-mathgroup at wolfram.com
Hello. I'm a user of Mathematica 3.0. A simple example of
what I'd like to do is as follows:
Suppose you have the finite series
S[i_]=Sum[x[k],{k,1,i}]
which is equal to x[1]+x[2]+...+x[i], where the total # of
terms i is left variable.
I'd like mathematica to calculate the difference
S[N]-S[N-1] = x[N]-x[0] .
I've tried commands like
Expand[S[N]-S[N-1]] and Simplify[S[N]-S[N-1]] ,
but mathematica doesn't simplify it as you would expect.
It basically does nothing. I suspect that it needs some
sort of clarification as to the nature of N (i.e. it's a
positive integer), but I'm not sure. Is there an easy
way for me to do what I'd like?
Thanks,
AC
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