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MathGroup Archive 2005

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Re: display of function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg58516] Re: display of function
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Tue, 5 Jul 2005 04:52:24 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, England
  • References: <dad7oo$t91$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Bosch, Darrell 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}
> 
> 
Hi Darrell,

Assuming that I have correctly understood what you tried to do, you 
could use either one of the following approaches:

In[1]:=
p = {0.3, 0.4, 0.3}
y = {10000, 20000, 30000}

Out[1]=
{0.3, 0.4, 0.3}

Out[2]=
{10000, 20000, 30000}

We take the product of the corresponding elements in each list

In[3]:=
p*y

Out[3]=
{3000., 8000., 9000.}

Finally, we take the sum of these products

In[4]:=
Plus @@ %

Out[4]=
20000.

This series of operations is indeed the dot product of p and y
In[5]:=
p . y

Out[5]=
20000.

If you need to use some other functions in place of *Plus* and *Times*, 
have a look at the *Inner* product.

Best regards,
/J.M.


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