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MathGroup Archive 2006

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Re: Function of several variables

  • To: mathgroup at smc.vnet.net
  • Subject: [mg72132] Re: Function of several variables
  • From: "Norbert Marxer" <marxer at mec.li>
  • Date: Wed, 13 Dec 2006 06:39:30 -0500 (EST)
  • References: <eljaik$7dv$1@smc.vnet.net>

Hi Troy

Try this

     f[p:Sequence[Subscript[_, _]...]] := Module[{}, 1/Total[{p}]]

Then

     f[Subscript[x, 1], Subscript[x, 2], Subscript[x, 3]]

will give you the inverted sum

1/(Subscript[x, 1] + Subscript[x, 2] +  Subscript[x, 3])

Of course you can apply any functions (inside Module) to your
subscripted indices.

Best Regards
Norbert Marxer
www.mec.li


tlhiv schrieb:

> I have created a list of variables that I would like to make a function
> in terms of by
>
> M = 4;
> X = Table[Subscript[x, i], {i, 1, M}]
>
> Now I would like to make a function f that is a function of each of
> these M variables.  If I were manually create this function without
> taking advantage of iterators, I would do something like
>
> f[Subscript[x,1]_,Subscript[x,2]_,Subscript[x,3]_,Subscript[x,4]_] =
> 1/(Subscript[x,1]+Subscript[x,2]+Subscript[x,3]+Subscript[x,4])
>
> However, my plan is to significantly increase M, and therefore I don't
> want to have to manually define f in this way.  I would like to define
> it in terms of the elements of X and use the Sum in the function
> definition.  In the end I'm going to be solving an optimization problem
> where I try to find the "optimal" choice for these elements of X.  Can
> someone offer a method for accomplishing this function definition?
>
> Thanks,
>
> --
> Troy Henderson
> Assistant Professor
> Department of Mathematical Sciences
> United States Military Academy
> http://www.tlhiv.org


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