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Re: Using "Sum" (i = 1 ... N) in a function definition
*To*: mathgroup at smc.vnet.net
*Subject*: [mg49724] Re: Using "Sum" (i = 1 ... N) in a function definition
*From*: Bill Rowe <readnewsciv at earthlink.net>
*Date*: Thu, 29 Jul 2004 07:45:03 -0400 (EDT)
*Sender*: owner-wri-mathgroup at wolfram.com
On 7/27/04 at 7:00 AM, wilhelm.rainer at gmx.net (Rainer) wrote:
>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
Rather than use Sum I would define MyFunc as follows
MyFunc[n_]:=Total@Take[MyData, n] (* using version 5.0 *)
or
MyFunc[n_]:=Tr@Take[MyData, n]
or
MyFunc[n_]:=Plus@@Take[MyData, n]
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