Re: Summation in Mathematica

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• Subject: [mg130611] Re: Summation in Mathematica
• From: Roland Franzius <roland.franzius at uos.de>
• Date: Fri, 26 Apr 2013 04:24:36 -0400 (EDT)
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```Am 24.04.2013 13:02, schrieb Ben Blomberg:
> Hello All,
>
> I am trying to understand a piece of code I found but I am stuck on this
> summation. This is part of a larger do loop over n.
>
>      UnderoverscriptBox[\(\[Sum]\), \(m = \(-10\)\),
> \(10\)]\(\(eigenfunctionsort[n, j]\)[\([m + 11]\)]
> Exp[I*2*\[Pi]*m*x/dp]\)\),{j,1,21}]
>
> What I mainly do not understand is  what is happening with the [m+11]. Is
> that being multiplied with eigen function sort with each step in the sum,
> or is that simply adding 11 to m at each step in the sum?

The piece of code should be read in InputForm

Sum[eigenfunctionsort[n, j][[m + 1]] * Exp[2 *\[Pi] *I *m *x /dp],
{m, -10,  10}]

In FullForm, eigenfunctionsort[n, j][[m + 1]]  means

Part[eigenfunctionsort[n, j],m+1],

the m+1-component of the vector of eigenfunctions probably with quantum
numbers n and j.

--

Roland Franzius

```

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