Re: A question about summation indicies

• To: mathgroup at smc.vnet.net
• Subject: [mg33112] Re: [mg33095] A question about summation indicies
• From: "Mark Morrissey" <mmorriss at ou.edu>
• Date: Sun, 3 Mar 2002 06:30:40 -0500 (EST)
• References: <200203011153.GAA27884@smc.vnet.net> <007a01c1c18f\$ef645a60\$e2b9eb94@dqb2301>
• Sender: owner-wri-mathgroup at wolfram.com

```Thank you very much Tomas - I looked at FullForm after I sent the message
and saw the underlying form was the reason (i.e. tehy're different).  What I
am trying (naively) to do is to derive through mathematica an equation for
the standard error of a raingauge network I put together about 10 years ago.
I'm finding that I have to learn more to do things algebracially. I'm still
struggling with why you have to define x first.  I'll do some more
experimenting.

Thanks - Mark

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

----- Original Message -----
From: "Tomas Garza" <tgarza01 at prodigy.net.mx>
To: mathgroup at smc.vnet.net
Subject: [mg33112] Re: [mg33095] A question about summation indicies

> 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
> Sent: Friday, March 01, 2002 5:53 AM
> Subject: [mg33112] [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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