Re: Defining a function
- To: mathgroup at smc.vnet.net
- Subject: [mg49999] Re: Defining a function
- From: koopman at sfu.ca (Ray Koopman)
- Date: Tue, 10 Aug 2004 06:02:57 -0400 (EDT)
- References: <cen7rv$h8$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
"PSi" <psinome at tee.gr> wrote in message news:<cen7rv$h8$1 at smc.vnet.net>...
> I want to compute the Sum[a[i, j]] as a function of k when
> 1 <= i <= m, 1 <= j <= n and i+j=k. The numbers m, n and
> the function a[i, j] are given. Is it possible to define such a
> function with Mathematica 4.1?
> Thanks, PSi
j=k-i : from i+j=k
1 <= k-i <= n : substitute k-i for j
-1 >= i-k >= -n : multiply by -1
k-1 >= i >= k-n : add k
k-n <= i <= k-1 : restate
f[k_] := Sum[a[i,k-i], {i, Max[1,k-n], Min[m,k-1]}]