5

When I write something like

x is a stochastic function of y:
    x ~ N(2y, 3)                      (1),

how do I refer back to that... non-equation? Do I still put "see Eq. (1)" although (1) is not an equation?

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    ...and why does there seem to be no LaTeX-like formatting on academia.stackexchange? – Johannes Bauer Jan 9 '14 at 11:11
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    To this point we have not had much need for it. Almost all of the questions that would require it are probably off-topic here and belong somewhere else (like Tex-LaTeX). Not every stack exchange site will need LaTeX - for example Seasoned Advice (about cooking). The Academia Meta is the place to bring up this issue if you want to pursue it. – Ben Norris Jan 9 '14 at 13:14
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    MathJax support isn't available here, because most questions on this site don't need such support. If the site doesn't need it, it doesn't use it. (Notably, the TeX site doesn't support MathJax, either!) – aeismail Jan 9 '14 at 13:15
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    I just asked this question on Academia Meta. BTW: I don't think MathJax should be supported by TeX, since most of the time people there want their code displayed, not interpreted. – Johannes Bauer Jan 10 '14 at 15:01
  • @aeismail and TeX.SX will of course never support MathJaX, it's even quite off-topic there ;) – yo' Jan 12 '14 at 20:43
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Mathematically you are true... it's not an equation. Technically I would say, that everything, that is display-style math and has a number attached for identification is called an equation in such contexts.

  • I'm accepting this answer because it seems to apply best to my field. The availability heuristic already told me that we probably call everything an equation, because I can't remember inequalities etc. being called anything else. Since someone else seems to concur and no-one seems to think otherwise I'm happy. – Johannes Bauer Jan 10 '14 at 14:49
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It seems that the right thing to do will depend on what's conventional in your field. In pure mathematics, it's standard to refer to all displayed equations, inequalities, etc. using just numbers in parentheses (for example, "using (2.1)", without specifying there whether (2.1) is an equation). You could add a descriptive noun if you'd like to emphasize it (e.g., "using equation (2.1)"), but you don't need to. If you do add a noun, it could be considered strange to refer to anything but an actual equation as an equation. This style of referencing displays creates no ambiguity, since citations use square brackets and all other numerical references have an attached noun or symbol to indicate whether they refer to a theorem, section, etc.: [1] is a citation, (1) is an equation or other display, Lemma 1 is a lemma, Section 1 is a section, etc.

The system described in the previous paragraph presumably doesn't apply to the author of the question, since abbreviations like "Eq. (1)" or "Ineq. (1)" are not standard in pure mathematics, which suggests he is in another field. However, it's worth keeping in mind that conventions vary between fields, so there won't be an absolute answer to this question. To know for sure what would look reasonable, it's important to know the context (i.e., the audience for the paper and where it might be published).

  • I'm in computer science, specifically in AI. We put Eq. (1) to distinguish from Fig. (1), Tab. (1) etc. Of course if most of what you refer to are equation-like things, then dropping the noun for only those does make sense. – Johannes Bauer Jan 10 '14 at 14:42
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    @JohannesBauer: You do not have "Figure (1)" or "Table (1)"; they are "Figure 1" and "Table 1". – Jukka Suomela Jan 12 '14 at 20:43
  • @JukkaSuomela good point. A matter of the LaTeX style, though, I should think. – Johannes Bauer Jan 15 '14 at 16:38
  • @JohannesBauer A matter of bad style, maybe. Even an enumerate item (1) should be referred to as "Item 1" instead of "Item (1)". – yo' Feb 24 '14 at 14:39
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If you absolutely don't want to use Eq. (1) for mathematical reasons (~ is not equal), I would suggest

See Formula (1)

although this is not conventional.

Someone suggested "See (1)". I personally would not use it because it has some ambiguity to me. Does it mean "See Sec. (1)" or something else?

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    As far as I can see in my research field (where LaTeX is standard), numbering within parentheses is only used for equation numbers, so there shouldn't be any ambiguity. But that surely doesn't hold globally. – Benedikt Bauer Jan 9 '14 at 12:44
  • @BenediktBauer I tend to agree with you. I still don't like (1) only, though. I tone down my answer a little bit. – scaaahu Jan 9 '14 at 12:53
  • @BenNorris I took out my comment about LaTex after I saw aeismail's and your comment. Sorry, my bad. – scaaahu Jan 9 '14 at 13:21
  • "Expression" is another option. – Noah Snyder Jan 12 '14 at 20:56
2

As mentioned in some other answers, and with some addendum. Five examples of the same text in different styles (please, excuse my English):

  1. We may now apply (15) to (13). From (12) we then see that (14) is satisfied.

  2. We may now apply Eq. (15) to Eq. (13). From Eq. (12) we then see that Eq. (14) is satisfied.

  3. We may now apply Eq. 15 to Eq. 13. From Eq. 12 we then see that Eq. 14 is satisfied.

  4. We may now apply Equation (15) to Equation (13). From Equation (12) we then see that Equation (14) is satisfied.

  5. We may now apply Equation 15 to Equation 13. From Equation 12 we then see that Equation 14 is satisfied.

(You can substitute "Eq." by "Ineq." etc., whatever you want.)

Such chains of links to equations are much common than for figures or tables. Now tell me in Examples 2 and 3 where the sentences stard and end. Yes, after a while, one sees that the sentence ends after "(13)", but it takes a lot of time to realize that. In Examples 4 and 5, the text gets unnecessarily long.

In my opinion, equations should be refered solely by their number in parentheses, references of course solely in brackets. For figures, enumerated lists, examples, sections, theorems etc., one should spell out the name (abbreviated or not, that's a personal taste) and add the number without any parentheses, even if it originally had some.

So a numbered list: "(1) apple; (2) banana" is still refered as: "In Item 2 we see that banana is a banana." If you refer items a lot, it's worth giving them a style that doesn't clash with the one for equations, like (a), (b), (c), ... or (i), (ii), (iii); then you can refer the items without the word "Item".

Final example:

Some solutions of (3) were obtained by Doe in [11]; we list them in Table 5 and they are plotted in Figure 1.

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