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Re: Using "Sum" (i = 1 ... N) in a function definition
*To*: mathgroup at smc.vnet.net
*Subject*: [mg49720] Re: Using "Sum" (i = 1 ... N) in a function definition
*From*: "Peltio" <peltio at twilight.zone>
*Date*: Thu, 29 Jul 2004 07:44:30 -0400 (EDT)
*References*: <ce5d8p$b4k$1@smc.vnet.net>
*Reply-to*: "Peltio" <peltioNOSP at Mdespammed.com.invalid>
*Sender*: owner-wri-mathgroup at wolfram.com
"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}];
I suggest that you use a delayed assignment in the definition of your
function MyFunct, here.
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
You can obtain the same result via
MyFunc[i_] := Plus @@ Take[MyData, i]
(in version 5 Total@ can be used instead of Plus@@)
cheers,
Peltio
Invalid address in reply-to. Crafty demunging required to mail me.
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