Vertical space using default display skip

Question

I have defined the following environment that tightens up equations of different environments, adding just one initial and one final space. For example, this code:

\documentclass{article}

\newenvironment{tight}
    {
    \vspace{\abovedisplayskip}
    \setlength{\abovedisplayskip}{0pt}
    \setlength{\abovedisplayshortskip}{0pt}
    \setlength{\belowdisplayskip}{0pt}
    \setlength{\belowdisplayshortskip}{0pt}
    }{
    \vspace{10.0pt plus 2.0pt minus 5.0pt}
    }

\setlength{\parindent}{4em}

\begin{document}

Sample text Sample text Sample text Sample text Sample text Sample text Sample text Sample text Sample text:
\begin{tight}
\begin{equation}
a = b^ 2 + c^2
\end{equation}
\begin{equation}
e^{j\theta} = \cos \theta + j \sin \theta
\end{equation}
\end{tight}
Sample text Sample text Sample text Sample text Sample text Sample text Sample text Sample text Sample text.

\end{document}

Gives this result:

There are two problems with the environment:

• As you can see from the example, the last \vspace is not placing the space as intended (unless I make a new paragraph, but I do not want that).
• I must manually define the parameters of the last \vspace, I do not know a way of saving the default skip parameters before setting them to zero.

My question is: is there a way fixing any of these problems?

Answer 1

You are trying to reinvent the wheel! 😉

Doing that with \vspace is not really the best choice and moreover the spacing you get will be very uneven.

The problem is solved by using gather:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

Sample text Sample text Sample text Sample text Sample text
Sample text Sample text Sample text Sample text:
\begin{gather}
a = b^ 2 + c^2
\\
e^{j\theta} = \cos \theta + j \sin \theta
\end{gather}
Sample text Sample text Sample text Sample text Sample text
Sample text Sample text Sample text Sample text.

\end{document}

It is possible with a tight environment, but I can't recommend doing it.

\documentclass{article}
\usepackage{amsmath}

\newenvironment{tight}
 {%
  \vspace{\abovedisplayskip}%
  \setlength{\savedbelowdisplayskip}{\belowdisplayskip}% save the value
  \setlength{\abovedisplayskip}{0pt}%
    \setlength{\abovedisplayshortskip}{0pt}%
    \setlength{\belowdisplayskip}{0pt}%
    \setlength{\belowdisplayshortskip}{0pt}%
 }{%
   \vadjust pre{\vskip\savedbelowdisplayskip}% the dirty trick!
   \ignorespacesafterend
 }
\newlength{\savedbelowdisplayskip}

\begin{document}

Sample text Sample text Sample text Sample text Sample text 
Sample text Sample text Sample text Sample text:
\begin{tight}
\begin{equation}
a = b^ 2 + c^2
\end{equation}
\begin{equation}
e^{j\theta} = \cos \theta + j \sin \theta
\end{equation}
\end{tight}
Sample text Sample text Sample text Sample text Sample text 
Sample text Sample text Sample text Sample text.

\end{document}

You can get tighter spacing also with gather by setting \jot to zero, but I don't recommend it either.

\documentclass{article}
\usepackage{amsmath}

\setlength{\jot}{0pt}

\begin{document}

Sample text Sample text Sample text Sample text Sample text
Sample text Sample text Sample text Sample text:
\begin{gather}
a = b^ 2 + c^2
\\
e^{j\theta} = \cos \theta + j \sin \theta
\end{gather}
Sample text Sample text Sample text Sample text Sample text
Sample text Sample text Sample text Sample text.

\end{document}