# Notation to describe vector

I want to describe a vector of n length, where each element is described by it's index. What is the correct notation?

As it is now, to describe the vector [ 1 4 9 16 ] i write:

$\{a^{2}\}_{a=1}^{4}$

But I can't remember if this is something i made up in my own mind.

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I think you mean [1 4 9 16]... –  Jesse Madnick Apr 14 '11 at 8:19
Using $\{ \ldots \}$ would suggest a set. You should use $( \ldots )$ instead. –  Zhen Lin Apr 14 '11 at 9:13

## 1 Answer

I will advise you to write $\mathbf{a} = (a_1,...,a_4 )$ where $a_i = i^2$. A little bit longer but correct.

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This is actually the notation I am trying to avoid since it has become very unpractical when dealing with a lot of vectors. Is my shorter notation wrong? –  user8111 Apr 14 '11 at 8:39
@Marc: What context do you want to use the notation in? Notations are largely invented for convenience, if it's convenient to you, it's a good notation. The only qualm a mathematician could have with it is the curly brackets which usually serve to denote sets. If you replace them by normal round brackets, that should be fine. –  Raskolnikov Apr 14 '11 at 9:02
I see, thanks for the help! –  user8111 Apr 14 '11 at 9:18
I also advise you to predefine this notation in the form with an explanation of the notation and then use the notation which you need. –  Ilya Apr 14 '11 at 9:28