Re: display of function

• To: mathgroup at smc.vnet.net
• Subject: [mg58531] Re: [mg58506] display of function
• From: "Carl K. Woll" <carl at woll2woll.com>
• Date: Wed, 6 Jul 2005 03:11:15 -0400 (EDT)
• References: <200507050557.BAA29432@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Darrell Bosch wrote:
>
> Dear Math Group:
>
>            The first equation below shows a function for u(y) which is
> the sum of the products of pi times yi.  In the following steps, I
> assign values of p and y.   How can I get Mathematica to display the
> numerical value of u for the given p and y values?  When I insert the
> u[y] command, I just get a repeat of the equation I have entered.
> Thanks for your suggestions.  This group is a great help.  Darrell
>
>
>
> u[y_] := Sum[Subscript[p, i]*Subscript[y, i],
>
>   {i, 1, n}]
>
>
>
> p = {.3,.4,.3}
>
>
>
> y={10000, 20000, 30000}
>
>

Darrell,

As others have mentioned, for this case the simplest approach is to use Dot:

u[y_] := p.y

Again, as others have mentioned, using Part instead of Subscript in your
method would work.

I just want to point out that it's possible to use subscripts in the way you
intended:

u[y_] := Sum[ p      * y      ,{i,1,n}]
[[i]]    [[i]]

The above is not working Mathematica code, you need to use 2D boxform input,
i.e., input the subscripts using Ctrl-_. In other words, when Mathematica
parses 2D boxform input where the subscript is a part specfication, then
Part is automatically used instead of Subscript. You can make things even
prettier by using \[LeftDoubleBracket] and \[RightDoubleBracket] instead of
[[ and ]].

Carl Woll
Wolfram Research

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