Given a tuple e=(x,y), how do I reference the 2nd item (y)?
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1Sometimes $p_2(e)$ is used to denote the 2nd projection. http://en.wikipedia.org/wiki/Projection_%28mathematics%29 – Martin Sleziak Apr 09 '11 at 10:34
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3Or just $e_2$ . – lhf Apr 09 '11 at 10:54
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3But, when you want to use one of these, explain it! You cannot assume the reader knows it already. – GEdgar Apr 09 '11 at 14:08
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1I have seen $\pi_2\left(e\right)$, too. – Apr 09 '11 at 19:26
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1Sometimes also $e^{(2)}$ and even $e^2$. – lhf Apr 11 '11 at 10:45
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1This does not directly answer your question, but as a more general remark: I find it quite handy to describe an $n$-tuple as $\mathbf{x}\in\mathbb{R}^n$ (note the bold font). Then the $i$th element can easily addressed with $x_i$. – B0rk4 Feb 06 '12 at 16:42
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I figured I would collect a number of the comments together into an answer so you would have something to accept (citing, so no one would hate on me for an plagiarism).
As with many types of mathematical notations, there are a number of possible variations here.
- Sometimes $p_2(e)$ or $\pi_2(e)$ is used to denote the 2nd projection (Martin Sleziak, FrancescoTurco).
- If you define an n-tuple as $\mathbf{x}\in\mathbb{R}^n$ (note the bold font), then the $i$th element can easily addressed with $x_i$ (Hauke Strasdat).
- Sometimes even $e^{(2)}$ or $e^2$ (lhf).
Just be sure you explain to the reader what you mean by the notation—don't assume he will understand (GEdgar).
