Too much vertical space when displaying formulas in LyX

Question

When I display formulas in LyX, it leaves way too much space between the text. The commands I have used are Insert -> Math -> Display Formula and Insert -> Math -> AMS multline Environment. However, the PDF looks exactly the same:

Is there a way to display formulas while not going beyond "double spaced"? Are there any packages to add which will avoid this problem?

EDIT: Problematic portion exported to Latex (plain)

    {\large \par}

\begin{multline*}
K_{0}(\theta)=\lbrace\langle m;b_{1},b_{2},\ldots\rangle_{\theta}:b_{j}\,\text{is eventually even and }\lim_{j\to\infty}b_{j}n_{j}\Vert n_{j}\theta\Vert=0\rbrace,\K_{1}(\theta)=\lbrace\langle m;b_{1},b_{2},\ldots\rangle_{\theta}:\sum_{j=1}^{\infty}|b_{j}|n_{j}||n_{j}\theta||<\infty\rbrace.
\end{multline*}

Answer 1

This picture is slightly different to the OP's one. The suggestions given below are used. The LaTeX code generated by LyX (with a few lines deleted) is:

\documentclass[12pt]{article}
\setlength{\parindent}{0pt}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{setspace}
\doublespacing
\begin{document}
each $j$. Given any integer $m$, $\left\langle m;b_{1},b_{2},\ldots\right\rangle _{\theta}:=\left(m\theta+\sum_{j=1}^{\infty}b_{j}n_{j}\theta\right)\mod1$
defines a point of $X$. Veech {[}4{]} defines
\begin{multline*}
K_{0}(\theta)=\left\{ \langle m;b_{1},b_{2},\ldots\rangle_{\theta}:b_{j}\,\text{is eventually even and }\lim_{j\to\infty}b_{j}n_{j}\left\Vert n_{j}\theta\right\Vert =0\right\} ,\\
K_{1}(\theta)=\left\{ \langle m;b_{1},b_{2},\ldots\rangle_{\theta}:\sum_{j=1}^{\infty}|b_{j}|n_{j}\left\Vert n_{j}\theta\right\Vert <\infty\right\} .
\end{multline*}
We have, corresponding to our elements of $K_{0}(\theta)$, a subset
of $\mathbb{R}$ which is a generalization of the Cantor set construction.
Define
\end{document}

First, looking at your LaTeX code, as Torbjørn T. and David Carlisle mentioned, the increased vertical space between the line containing "Veech [4]" and the multiline environment comes from a new line. In LyX you can make end of paragraphs visible under "Tools > Look & Feel > Display" otherwise the new line is invisible. Anyway, put the cursor directly after the s in "Veech [4] defines" and press Delete once to delete the new line. Note (or messure) that the distance between the baselines of "Veech [4]" and "K_0(\theta)" is the same as the distance between "K_1(\theta)" and "We have, corresponding...".

Second, looking into my crystal ball I tend to see

1. that the LaTeX code and the picture do not match, that is, for the picture the new lines in front of and after the multiline environment were removed;

2. that the font size is set to "Large" for parts of your document (or your entire document?) (font size "Large" in LyX corresponds to \large in LaTeX, as "Larger" corresponds to \Large ...);

3. that the line spacing is set to "Double".

4. that matching parentheses / delimiters were forgotten.

Not sure whether all points are true; just my guess. My suggestions are

1. (In LyX, there is also "View Source" to see the generated LaTeX code.) If there were a mismatch, maybe update the question.

2. Instead of using "Large" font size, "Reset" the font size to use "Normal" font and change "Fonts > Base Size" under "Document > Settings..." to 12pt. The default size corresponds usually to 10pt. Hence, the font size will not change ("10pt + \large = 12pt", see also here) but the width of the document will be adjusted differently for 12pt.

3. There are several rules in typography to make a text look better, although one might object to them at first. LaTeX (well, LyX is generating LaTeX code) knows about them and thinks some space around display math (e.g. multiline environment) looks better. This could also be a reason.

4. You have operators like "sum" in the formulas. Instead of using ( and ) you should consider using delimiters in math mode. (Use "Insert > Math > Delimiters" or simple the short cuts Alt+M ( or Alt+M < ...). Then the parentheses will be scaled and also some (a tiny) space will be inserted. Especially, this should be done with the ||norm||. Otherwise how to read your formula: this way | b |n| |n\theta| | or that way |b| n ||n\theta||??

Answer 2

{\large \par}

{\large 
\begin{multline*}

math displays should not be separated from the surrounding paragraph by a blank line or \par and you have both here. I don't use lyx but you need to configure it not to insert these paragraph breaks.