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RE: Using "Sum" (i = 1 ... N) in a function definition
*To*: mathgroup at smc.vnet.net
*Subject*: [mg49692] RE: [mg49666] Using "Sum" (i = 1 ... N) in a function definition
*From*: "Ellis, George" <George.Ellis at Cognos.COM>
*Date*: Thu, 29 Jul 2004 07:42:56 -0400 (EDT)
*Sender*: owner-wri-mathgroup at wolfram.com
Rainer,
I do not know why you would want to do this; so my response below may be
off target. Nonetheless, what about this? (The function "Total" in
version 5.0, in this case, provides the equivalent functionality -- as
would "Apply[Plus,data]" in earlier versions).
In[10]:= (8:59:39 on 7/27/04)
data=Range[10];
Sum[data[[x]],{x,Length[data]}]
Out[11]= (8:59:39 on 7/27/04)
55
In[9]:= (8:59:21 on 7/27/04)
Total[data]
Out[9]= (8:59:21 on 7/27/04)
55
Regards,
George
-----Original Message-----
From: Rainer [mailto:wilhelm.rainer at gmx.net]
To: mathgroup at smc.vnet.net
Subject: [mg49692] [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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