\abovedisplayskip and \belowdisplayskip

\abovedisplayskip and \belowdisplayskip

[Troy Henderson]

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It is my understanding that \abovedisplayskip and \belowdisplayskip should
adjust how much (rubber) spacing that is allowed between display math
formulas.  I have attached a ConTeXt file (bug.tex) that seems to indicate
that setting these skips does not affect this (rubber) spacing.  I have
also translated this ConTeXt file line-by-line to a LaTeX file (bug.ltx)
and attached it.

Both files produce a PDF (using `context bug.tex` and `pdflatex bug.ltx`)
in which the spacing between the formula changes from page 1 to page 2
simply by adding the final formula.  However, by changing \adjustdisplay{0}
to \adjustdisplay{1}, the LaTeX file produces a 3 page document where the
spacing between formula does not change (as expected) on the first two
pages and thus requires a third page to typeset the final formula.
However, making this same adjustment in the ConTeXt file does not seem to
affect the output.

I would appreciate any thoughts as to why this is happening, and I would
equally appreciate a solution to keeping the spacing the same in the
ConTeXt file and thus bumping that last formula to a third page.

Troy Henderson

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\documentclass{minimal}
\usepackage[paperwidth=600pt,paperheight=450pt]{geometry}

\def\adjustdisplay#1 {
	\ifnum#1>0
		\newdimen\mydimen
		\mydimen\abovedisplayskip \abovedisplayskip\mydimen
		\mydimen\belowdisplayskip \belowdisplayskip\mydimen
	\fi
}

\def\foo{
	\vskip0.5ex
	\[\frac{x}{1} = \frac{1}{x-1}\]
	\vskip0.5ex
	\[x(x-1)=1\]
	\vskip0.5ex
	\[x^2-x=1\]
	\vskip0.5ex
	\[x^2-x-1=0\]
	\vskip0.5ex
	\[x=\frac{1+\sqrt{5}}{2},\frac{1-\sqrt{5}}{2}\]
}

\begin{document}

	\pagestyle{empty}
	\fontsize{20}{24}\selectfont
	\adjustdisplay{0}

	\foo

	\clearpage

	\foo\vskip0.5ex
	\[\phi = \frac{x}{1} = x =\frac{1+\sqrt{5}}{2} \approx 1.618\]

\end{document}

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Re: \abovedisplayskip and \belowdisplayskip

[Aditya Mahajan]

On Thu, 6 Sep 2012, Troy Henderson wrote:

> It is my understanding that \abovedisplayskip and \belowdisplayskip should
> adjust how much (rubber) spacing that is allowed between display math
> formulas.  I have attached a ConTeXt file (bug.tex) that seems to indicate
> that setting these skips does not affect this (rubber) spacing.  I have
> also translated this ConTeXt file line-by-line to a LaTeX file (bug.ltx)
> and attached it.
>
> Both files produce a PDF (using `context bug.tex` and `pdflatex bug.ltx`)
> in which the spacing between the formula changes from page 1 to page 2
> simply by adding the final formula.  However, by changing \adjustdisplay{0}
> to \adjustdisplay{1}, the LaTeX file produces a 3 page document where the
> spacing between formula does not change (as expected) on the first two
> pages and thus requires a third page to typeset the final formula.
> However, making this same adjustment in the ConTeXt file does not seem to
> affect the output.
>
> I would appreciate any thoughts as to why this is happening, and I would
> equally appreciate a solution to keeping the spacing the same in the
> ConTeXt file and thus bumping that last formula to a third page.

ConTeXt uses spacebefore and spaceafter keys to adjust the spacing around 
formulas. The values of these keys are fed to `\blank[...]` so they can be 
any value that `\blank[...]` accepts (none, small, medium, big, etc., or a 
valid TeX dimen)

So, you should use something like

\setupformulas[spacebefore=..., spaceafter=...]

or if you only want to change the space around specific formulas

\defineformula[big][spacebefore=big,spaceafter=big]

and then use

\startbigformula ... \stopbigformula.

Aditya

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___________________________________________________________________________________

Re: \abovedisplayskip and \belowdisplayskip

[Troy Henderson]

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>
> \setupformulas[spacebefore=..., spaceafter=...]
>

This still does not quite fix my problem.  If spacebefore/after are set to
a reasonable value in the previously attached ConTeXt file, the spacing
changes very slightly (probably because of some rubber length) between the
formula from page 1 to page 2.

Troy

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