Re: Using "Sum" (i = 1 ... N) in a function definition
- To: mathgroup at smc.vnet.net
- Subject: [mg49718] Re: Using "Sum" (i = 1 ... N) in a function definition
- From: BobHanlon at aol.com
- Date: Thu, 29 Jul 2004 07:43:41 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Use SetDelayed (:=) in the definition of the function rather than Set (=)
MyData = {3,2,4,5,6};
MyFunc[i_] := Sum[MyData[[j]],{j,1,i}];
MyFunc /@ Range[Length[MyData]]
{3, 5, 9, 14, 20}
Bob Hanlon
> In a message dated Tue, 27 Jul 2004 11:11:21 +0000 (UTC),
> wilhelm.rainer at gmx.net writes: 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 ...?
>