Lower the period following a display style fraction

Question

I dislike the look of the output of the following code because the period mark following the fraction looks confused (to my eyes, at least), almost like it's trying to be a degree symbol. I wish that it was sitting on the same (invisible horizontal) line that the denominators are sitting on, only I don't want it to be inside of the denominator (that is, I don't want to write $$\frac{S}{D} = \frac{x}{360.}$$ rather than $$\frac{S}{D} = \frac{x}{360}.$$), because that would awkwardly extend the fraction line above the period.

How can I place the period on the outside of the fraction such that it is at the same vertical level as the period in $$\frac{S}{D} = \frac{x}{360.}$$?

\documentclass{article}
\usepackage{amsmath}
\begin{document}
Suppose I have something like $$\frac{S}{D} = \frac{x}{360}.$$
\end{document}

(Note: A closely related question is raised at Vertical position of punctuation following fractions in display-style equations, but there is no talk there of dropping the period to the floor, which is what I want.)

Another quick and dirty hack: \frac{x}{300\rlap{\,.}}. But really, the period should be on the main baseline. That is what a copyeditor for a math publisher would require. — barbara beeton, Jun 12 '23 at 23:28
What if the displayed equation ends with a double fraction, i.e., something like \frac{\frac{a}{b}}{\frac{c}{d}}? Should the period be placed on the baseline of the denominator of the denominator? (I hope not...) — Mico, Jun 12 '23 at 23:29

score 1 · Accepted Answer · answered Jun 13 '23 at 09:18

I see nothing wrong in the second example (just normal punctuation), but also the third example may be appealing (thin space before the period).

I can see no reason for lowering the period, like in the first example: it's definitely out of place there.

\documentclass{article}
\usepackage{amsmath}
\newlength{\lowerpunct}
\newcommand{\finalfrac}[3]{%
  % #1 = numerator, #2 = denominator, #3 = punctuation
  \settodepth{\lowerpunct}{$\displaystyle\frac{#1}{#2}$}%
  \frac{#1}{#2}%
  \raisebox{-\lowerpunct}{#3}%
}
\begin{document}
Suppose I have something like
[
\frac{S}{D} = \finalfrac{x}{360}{.}
]
Suppose I have something like
[
\frac{S}{D} = \frac{x}{360}.
]
Suppose I have something like
[
\frac{S}{D} = \frac{x}{360},.
]
\end{document}

Lower the period following a display style fraction

1 Answers1