Comma after equation [closed]

Question

I have seen different ways in papers to put comma after equation.

1. right after the equation:

   

2. right before where:

   

3. no comma at all:

   

Which way should I choose? Which way is more standard?

Answer 1

The first version is usually correct, the second is always wrong, sometimes the third is natural. Equations should read as part of the sentence in which they lie, and punctuation should follow accordingly. Usually in a sentence of the form

Consider the equation a=b, where b is convex.

there will be a comma before the where clause. If the equation is longer or important enough, so that it is displayed, you should follow the same pattern

Consider the equation

a=b,

where b is convex.

Similarly, final full stops (.) should be included in the display if the sentence ends there

This leads to the desired equation

a=b.

An example without puctuation could be

The distribution

D = \ker\Omega^1(S)

on Q is integrable.

Answer 2

I generally agree with Andrew that option (1) is preferred, since it fits most common mathematical style, and that (2) is unacceptable, but the analogy he makes between inline and set-off punctuation is not so close, and it is common to omit punctuation with set-off content where it would be included if that content was given inline.

For example, commas/ semicolons nearly always separate items in lists inline, but most often not when set off as bullet points. Likewise, logical punctuation (named by Ben Yagoda, The Rise of "Logical Punctuation", Slate) insists that punctuation should not appear in a set-off quote if it was not in the quoted text, even though logical punctuation would require, say, a comma or full stop after the closing quote mark for the quotation inline.

So omitting punctuation as per option (3) is perfectly coherent. Just be aware that it is not the dominant practice and that you need to be consistent.