General ⇒ Another Question about the align environment

[avp3000]

Hello,

Here is an example:

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\documentclass[10pt]{article}
\usepackage[a4paper,pagesize]{typearea}

\usepackage[english,ngerman]{babel}
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage{amsmath}

\usepackage{blindtext}
\usepackage[pdftex]{graphicx}
\usepackage{color}

\begin{document}

\blindtext
\begin{align*}
\pi_{i}(y_{i},y_{-i}) &= (1 - y_{i} - \sum_{j \neq i} y_{j})y_{i}\\
\Longrightarrow \quad \dfrac{\partial\pi_{i}}{\partial y_{i}} & = 1 - 2y_{i} - \sum_{j \neq i} y_{j} = 0 \\
\text{\textcolor{red}{Nash--Gleichgewicht}:}\\
y_{i}^{\ast} &= \dfrac{1}{(n+1)}\\
\Longrightarrow \qquad Y^{\ast} &= \frac{n}{(n+1)}
\end{align*}
\blindtext
\end{document}

I want to do several things:

1. I want that no empty lines appear between the equations and the two blind texts. I know it doesn't look good, but I need to do this in other situations.
2. I want to align "Nash--Gleichgewicht" to the left. Is there a way to starn an align* environment, than end it and have some normal text and than start the align environment again, but in a way that the equal (=) signs are abouve each other?

[Stefan Kottwitz]

Hi Alexander,

1. like in the other thread and in the modified example below,
2. use \intertext.

I modified the code, here without the preamble that wasn't modified:

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\begin{document}
\setlength{\abovedisplayskip}{0pt}
\setlength{\abovedisplayshortskip}{0pt}
\setlength{\belowdisplayskip}{0pt}
\setlength{\belowdisplayshortskip}{0pt}
\setlength{\jot}{0pt}

\blindtext
\begin{align*}
\pi_{i}(y_{i},y_{-i}) &= (1 - y_{i} - \sum_{j \neq i} y_{j})y_{i}\\
\Longrightarrow \quad \dfrac{\partial\pi_{i}}{\partial y_{i}} & = 1 - 2y_{i} - \sum_{j \neq i} y_{j} = 0 \\
\intertext{\textcolor{red}{Nash--Gleichgewicht}:}
y_{i}^{\ast} &= \dfrac{1}{(n+1)}\\
\Longrightarrow \qquad Y^{\ast} &= \frac{n}{(n+1)}
\end{align*}
\blindtext
\end{document}

Stefan

[avp3000]

One more question - what is the default value of \abovedisplayskip? Sometimes it's really useful changing this, but the disadvantage is, it screws the equations on the rest of the presentation. I would be very glad to know the default value, because in this case I can change it at the beginning of the slide and then turn it back to it's default value at the end of the slide. Thank you.

[Stefan Kottwitz]

Hi Alexander,

the value of \abovedisplayskip will be shown in a document if you write

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\the\abovedisplayskip

It will be written to the logfile if you use \showthe:

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\showthe\abovedisplayskip

I get 10.0pt plus 2.0pt minus 5.0pt with the article class.

Instead of using this value I would prefer to define a new length command and save the length of \abovedisplayskip to it for later use. If the change is needed just for a small range it's easier to limit the change of \abovedisplayskip by \begingroup ... \endgroup.
Above advice is valid for other lengths too, of course.

Stefan