RE: Using "Sum" (i = 1 ... N) in a function definition

*To*: mathgroup at smc.vnet.net*Subject*: [mg49707] RE: [mg49666] Using "Sum" (i = 1 ... N) in a function definition*From*: "David Park" <djmp at earthlink.net>*Date*: Thu, 29 Jul 2004 07:43:23 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Rainer, MyData = {3, 2, 4, 5, 6}; MyFunc[i_] := Sum[MyData[[j]], {j, 1, i}]; MyFunc[1] MyFunc[2] MyFunc[3] 3 5 9 You need the DelayedSet, :=, instead of Set, =. Otherwise Mathematica tries to evaluate the Sum statement immediately, which it can't do because it doesn't yet have a value for i. David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: Rainer [mailto:wilhelm.rainer at gmx.net] To: mathgroup at smc.vnet.net I was trying to define a function using the Sum command in the following way (simplified example): MyData = {3,2,4,5,6}; MyFunc[i_] = Sum[MyData[[j]],{j,1,i}]; As you can see, the idea is to use the length of the list (i) as a variable in the function definition, such that MyFunc[1] = 3 MyFunc[2] = 3 + 2 = 5 MyFunc[3] = 3 + 2 + 4 = 9 etc. Mathematica does not like the abobe statements, and prints the following error message: "Part specification K$394 is neither an integer nor a list of integers." Does anybody know how to define (correctly) such a function. Should be possible ...? Thanks Rainer