I want to duplicate the compact look of G. K. Batchelor's fluid dynamics book. Where a paragraph terminates such that the mathematical expression can collapse up into the vertical space of the paragraph, the expression moves up. If that makes no sense, see it on Google Books.
align environment do this automatically? Or do I need to use another environment? I'm not aware of any way to do this automatically.
Here is a LaTeX approach at duplicating the typesetting in your link, as well as using @morbusg's
-.5\baselineskip(plus some glue):
geometrywas used to reduce the margins and mimic the linked output.
The only difference in the output was from typesetting the line that has a centered alignment with respect to the text block, while still having text left-aligned ("Moreover," in this case). Some "trickery" (via
\rlap) was used to obtain this, but that could also have been what the author did in their markup. As @egreg mentioned in comment, the use of
\leavevmodeis necessary if the paragraph was preceded by a blank line. As such, and for completeness (since it does no harm here...), I've added
From a pedagogical point of view, the use of
\abovedisplayshortskipis taken from the width of the (single) last line in the preceding paragraph. As such, it would take more than just modifying
\abovedisplayshortskipto accommodate the display presented in your link for a general use-case when the previous paragraph consists of a single line, unless you're willing to do some compacting yourself using manual intervention (as I did in my example).