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Given a tuple e=(x,y), how do I reference the 2nd item (y)?

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    $\begingroup$ Sometimes $p_2(e)$ is used to denote the 2nd projection. en.wikipedia.org/wiki/Projection_%28mathematics%29 $\endgroup$ Apr 9, 2011 at 10:34
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    $\begingroup$ Or just $e_2$ . $\endgroup$
    – lhf
    Apr 9, 2011 at 10:54
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    $\begingroup$ But, when you want to use one of these, explain it! You cannot assume the reader knows it already. $\endgroup$
    – GEdgar
    Apr 9, 2011 at 14:08
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    $\begingroup$ I have seen $\pi_2\left(e\right)$, too. $\endgroup$
    – user112679
    Apr 9, 2011 at 19:26
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    $\begingroup$ Sometimes also $e^{(2)}$ and even $e^2$. $\endgroup$
    – lhf
    Apr 11, 2011 at 10:45

1 Answer 1

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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).

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