Typesetting a formula

August 31, 2006 4:21 PM

Where can I find typographic conventions for algebra? Specifically...

Here are two questions:

(1) Say just hypothetically that the number of people now (n) at 0 hours is the sum of the number of people (n) 12 hours ago and twice the number of people 24 hours ago. From what I can tell, I typeset the formula like this:

n = n₁₂ + 2n₂₄

As you can see, the 2 multiplier is nonitalicized, I italicized n, but left the subscripts nonitalicized. A book I have has them that way. Is that right?

(2) How do you handle a special category of number, for instance, the number of people (n) in the bathroom (b), say n_b. Would the number of people in the bathroom 24 hours ago be n_b24? Or should I invent a different variable, such as b?

posted by chef_boyardee to Science & Nature (6 answers total)

Sub-subscripts, man. n_{b_24} in LaTeX.
posted by mr_roboto at 4:38 PM on August 31, 2006

Your italicizing and non-italicizing is fine. However, I'm not sure about your choice of variables.

A subscript on a variable usually indicates that the subscripted variables bear some relation to each other. For instance,

t = time

t_event = t_end - t_start

Right? All the t's could be times in seconds. If you start measuring at 11 seconds, and end measuring at 42 seconds, the time of the event is 31 seconds, right? I chose "t" as the variable for a reason, to be reminiscent of the word "time".

Or say:

a = (v_end - v_start) / (t_end - t_start)

Acceleration equals the change in velocity per the change in time. Right? I'm intentionally choosing variable letters that have meaning, to relate the problem to a real-world situation. Since I have two different velocities, I need subscripts to distinguish my "v"'s from each other.

For your example, the number of people in the bathroom 24 hours ago, 12 hours ago, and now, don't seem to have any real relation to each other. n₁₂ and n₂₄ are rather confusing. Nor is it apparent *why* the number of people present now bears any mathematical relationship to the number of people present 12 or 24 hours ago. Unless there's some good reason to use subscripts, you might do better to avoid them.

On preview: it is legitimate to use multiple subscripts: n_{thisisstupidbutlegal}

But please don't.
posted by jellicle at 4:46 PM on August 31, 2006

I'd be tempted to write this as if n was a formula:

n(t)

where t is the time ago in hours and 0 is now. So your first example would be:

n(0) = n(12) + n(24)

Then if you wanted to have number-of-people-in-the-bathroom-twenty-four-hours-ago, you could just have:

n_b(24)
posted by chrismear at 4:55 PM on August 31, 2006

In such formulas, typically all letters are italicized, even if they are in subscripts, while numbers are not.

I'd say it's OK to use n₂₄ for the number of people in bathroom 24. But, if you only have one bathroom, and the number of people changes depending on the time, then I'd use something like b(12) for the number of people at time 12 and b(13) for the number of people at time 13. The notation b(_) suggests that b is a function, and it has some particular value for each time.

If you're going to be typesetting more than just a couple of formulas here and there, you really want to use LaTeX, as mr_roboto mentioned. If you do, then you just pick a standard math package, and then you don't have to worry about what's italicized and what's not - the program does that for you.

Finally, if you want to see how mathematics articles are typeset, you can look at some preprints at the ArXiv.
posted by epimorph at 5:35 PM on August 31, 2006

here's part of the springer style guide for mathematical notation, and here's the AIP style guide for physics journals. they might help.
posted by sergeant sandwich at 5:46 PM on August 31, 2006

NIST has a style guide that I find very useful.
posted by grouse at 12:40 AM on September 1, 2006