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MathGroup Archive 2004

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

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49691] Re: [mg49666] Using "Sum" (i = 1 ... N) in a function definition
  • From: Matthias.Bode at oppenheim.de
  • Date: Thu, 29 Jul 2004 07:42:55 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello Wilhelm,

try:

mydata = {3, 2, 4, 5, 6}; 
myfunc[n_] := Plus @@ Take[mydata, 
    n]

Best regards,
Matthias Bode
Sal. Oppenheim jr. & Cie. KGaA
Untermainanlage 1
D-60329 Frankfurt am Main
GERMANY
Tel.: +49(0)69 71 34 53 80
Mobile: +49(0)172 6 74 95 77
Fax: +49(0)69 71 34 95 380
E-mail: matthias.bode at oppenheim.de
Internet: http://www.oppenheim.de



-----Ursprüngliche Nachricht-----
Von: wilhelm.rainer at gmx.net [mailto:wilhelm.rainer at gmx.net] 
Gesendet: Dienstag, 27. Juli 2004 13:01
An: mathgroup at smc.vnet.net
Betreff: [mg49666] Using "Sum" (i = 1 ... N) in a function definition


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


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