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Let us have a look at the following minimal example:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
This is the first line.
% \begin{gather*} x^2 + y^2 = z^2. \end{gather*}
\begin{displaymath} x^2 + y^2 = z^2. \end{displaymath}
This is the second line.
\end{document}

If uncomment the displaymath and comment the gather* part, then the vertical spacing changes: the AMS math environment takes up space much more generously.

I know that the AMS environments have adaptive vertical spacing to some extent, but I don't know how much. I don't know whether the plain display math environment ever adapts or is just set a minimum.

I can imagine a situation, such as where the article is supposed to be within a page limit and using either of these environments, depending on their vertical spacing behavior, may lead to problems.

Q: What are the rules that governs the vertical spacing in plain displaymath and AMS math environments?

shuhalo
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  • Are you familiar with the posting What are the differences between $$, \[, align, equation and displaymath? – Mico Sep 24 '23 at 05:59
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    A separate question: Are you familiar with the following simple piece of advice: "Don't use the multiline environments of the amsmath package (such as align and gather) for single-line display math material"? Incidentallly, what's the basis for your claim that "the AMS environments have adaptive vertical spacing to some extent"? – Mico Sep 24 '23 at 06:03
  • @Mico: this is a minimal working example for technical illustration, and my claim is based on practical observation. – shuhalo Sep 24 '23 at 06:14
  • @Mico: I was not aware of it. However, the posting, while very informative, does not seem to address the final question about what controls the vertical spacing in AMS environments. – shuhalo Sep 24 '23 at 06:15

1 Answers1

5

The space above a math display is either \abovedisplayskip or \abovedisplayshortskip depending on whether the last line of the previous paragraph overlaps the equation.

However AMS alignments are always technically full width whatever their visible content so always overlap and the short skip is thus never used.

Don't use multi-line displays for single line equations, use \[ or equation

David Carlisle
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