Re: A question about summation indicies

• To: mathgroup at smc.vnet.net
• Subject: [mg33111] Re: [mg33095] A question about summation indicies
• From: Tomas Garza <tgarza01 at prodigy.net.mx>
• Date: Sun, 3 Mar 2002 06:30:39 -0500 (EST)
• References: <200203011153.GAA27884@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Yes, it does. x has not ben defined, so let's take a look at what's going on
using FullForm (BTW, try not use capital letters for your variables; they
are supposed to be reserved for Mathematica functions):

In[1]:=
FullForm[Sum[x[i], {i, 1, n}]]
Out[1]//FullForm=
Sum[x[i], List[i,1,n]]

Something similar happens for the Sum with j instead of i, and it is obvious
that List[i, 1, n] is not equal to List[j, 1, n], and this is why you don't
get a "True". However, if you have a previously defined x, for example

In[2]:=
x[i_] := 2^i

then

In[3]:=
Sum[x[i], {i, 1, n}] == Sum[x[j], {j, 1, n}]
Out[3]=
True

Tomas Garza
Mexico City

----- Original Message -----
From: "Mark Morrissey" <mmorriss at ou.edu>
To: mathgroup at smc.vnet.net
Subject: [mg33111] [mg33095] A question about summation indicies

> Hi - I have a simple question that probably has a simply answer.
>
> Why does Sum[x[i],{i,1,N}]==Sum[x[j],{j,1,N}]
>
> not produce a 'True' in Mathematica???
>
>
> Mark Morrissey
> Associate Professor of Meteorology
> Associate State Climatologist for Research
> University of Oklahoma
> 710 Asp Ave, Suite 8
> Norman, OK 73069
> 405 447-8412
>
>
>

```

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