2

If I use \begin{align*}...\end{align*} and out of it I write a text then there is a big vertical space between the text and the mentioned environment. Why is there that space? And how can I erase it? Also in this case I think that the vertical space is too much. For example in tabular environment or other environments there is much less vertical space. Why is align environment different?

\documentclass[12pt]{article}
\usepackage[top=0.3in, bottom=1.2in, left=0.8in, right=0.8in]{geometry}

\usepackage{multicol}

\usepackage[utf8]{inputenc}

\setlength{\parindent}{0cm}

\usepackage{setspace}

\usepackage{xltxtra}
\usepackage{xgreek}
\setmainfont[Mapping=tex-text]{GFSDidot.otf}
\setsansfont[Mapping=tex-text]{GFSDidot.otf}

\usepackage[fleqn]{amsmath}
\usepackage{unicode-math}

\setlength{\mathindent}{0cm}

\newcommand{\3}{\vspace{0.3cm}}

\title{}
\author{}
\date{}

\begin{document}

\begin{multicols*}{2}


70
\begin{align*}
&e^{jz}=\cos z+j\sin z\\
&\cos z=(1/2)(2\cos z)=\\
&=(1/2)(2\cos z+j\sin z-j\sin z)=\\
&=(1/2)(\cos z+j\sin z+\cos z-j\sin z)=\\
&=(1/2)(e^{jz}+e^{-jz})
\end{align*}


\end{multicols*}
\end{document}

enter image description here

70

\begin{align*}
&e^{jz}=\cos z+j\sin z\\
&\cos z=(1/2)(2\cos z)=\\
&=(1/2)(2\cos z+j\sin z-j\sin z)=\\
&=(1/2)(\cos z+j\sin z+\cos z-j\sin z)=\\
&=(1/2)(e^{jz}+e^{-jz})
\end{align*}

enter image description here

Adam
  • 4,684
  • This is not a duplicate question. The document class is article and the font size is 12. According to Barbara Beeton's answer, the only solution is to set font size to 10 (by using \normalsize). Therefore, I do not see a solution to this question either here or at the "duplicate" question. – Sony Aug 18 '14 at 14:13

2 Answers2

5

don't leave a blank line between text and any display math -- that adds extra space because you are saying "start a new paragraph here."

if you have just a short bit of text between lines of an aligned display, you can use \intertext:

text above
\begin{align}
 a &= b + c\\
   &= d + e\\
 \intertext{because}
   &= f + g
\end{align}

edit: the amount of space above a display is determined by the setting of \abovedisplayskip. the default value for \abovedisplayskip is set by latex.ltx to 12pt plus 3pt minus 9pt. this can be overridden by the document class being used, but article doesn't do so unless \normalsize is invoked, in which case the basic length is set to 10pt for 10pt text.

other document classes have different settings. amsart (which is the class that amsmath was originally designed to cooperate with) sets \abovedisplayskip=.7\baselineskip plus .7\baselineskip (no minus component), or 8.4pt for 10pt text.

why article and the other "basic" latex document classes use the larger value is a design decision, presumably by leslie lamport; i'm unable to explain any reasons for that decision.

barbara beeton
  • 88,848
3

There are four predefined lengths, which control the vertical whitespace of displayed formulas:

\abovedisplayskip=12pt plus 3pt minus 9pt
\abovedisplayshortskip=0pt plus 3pt
\belowdisplayskip=12pt plus 3pt minus 9pt
\belowdisplayshortskip=7pt plus 3pt minus 4pt

The "short" version is used for equation, when the last line of text is short.

Tahtisilma
  • 2,396