# Latex-Beamer: overprint-environment wobbles

I am new to the beamerclass and I am currently trying to write a presentation containing lots of derivations. On one point I want to overlay a derivation by its conclusion and I use the overprint-environment. The problem is that the environment shifts the whole derivation downwards so that the last line is only partially visible. How can I avoid this? There is a workaround by making a second frame, copying the whole content and replacing the derivation with the conclusion, but I do not consider that "elegant" and it would falsify the frame counter.

I would appreciate any help.

A minimal example is attached:

\documentclass[xcolor=dvipsnames]{beamer}
\mode<presentation>

\usepackage[ngerman]{babel}
\usepackage[utf8]{inputenc}
\usepackage{amsfonts,amsmath,amssymb,amsthm}

\DeclareMathOperator{\Var}{Var}
\DeclareMathOperator{\E}{\mathbb E}

\title{Dummy-Titel}
\subtitle{Dummy-Untertitel}
\author{Autor}

\date{\today}

\begin{document}

\begin{frame}{Erwartungswert}
\begin{itemize}
\item $\E(X_{t+1} | X_t = i) = \sum_{j=0}^{2N} j \cdot P(X_{t+1}=j | X_t = i)$
\item $X_{t+1}$ binomialverteilt mit Parametern $n=2N$ und $p=\frac{i}{2N}$:
$\Rightarrow \E(X_{t+1} | X_t=i) = n \cdot p = i$
\item Martingal-Eigenschaft: $\E(X_{t+1} | X_t) = X_t$
\end{itemize}
\begin{overprint}
\onslide<1>
\begin{align*}
\E(X_t) &= \E(\E(X_{t+1} | X_t)) = \sum_{i=0}^{2N} E(X_{t+1} | X_t = i) \cdot P(X_t = i) \\
&= \sum_{i=0}^{2N} \left( \sum_{j=0}^{2N} j \cdot P(X_{t+1}=j | X_t = i) \right) \cdot P(X_t = i) \\
&= \sum_{j=0}^{2N} j \cdot \left( \sum_{i=0}^{2N} \cdot P(X_{t+1}=j , X_t = i) \right) \\
&= \sum_{j=0}^{2N} j \cdot P(X_{t+1}=j) = \E(X_{t+1})
\end{align*}
\onslide<2>
\begin{equation*}
\Rightarrow \E(X_0) = \E(X_1) = \E(X_2) = \ldots
\end{equation*}
\end{overprint}
\end{frame}
\end{document}

-

Not very elegant perhaps, but you could simply add some negative vspace before the align*.

\documentclass[xcolor=dvipsnames]{beamer}
\mode<presentation>

\usepackage[ngerman]{babel}
\usepackage[utf8]{inputenc}
\usepackage{amsfonts,amsmath,amssymb,amsthm}

\DeclareMathOperator{\Var}{Var}
\DeclareMathOperator{\E}{\mathbb E}

\title{Dummy-Titel}
\subtitle{Dummy-Untertitel}
\author{Autor}

\date{\today}

\begin{document}

\begin{frame}{Erwartungswert}
\begin{itemize}
\item $\E(X_{t+1} | X_t = i) = \sum_{j=0}^{2N} j \cdot P(X_{t+1}=j | X_t = i)$
\item $X_{t+1}$ binomialverteilt mit Parametern $n=2N$ und $p=\frac{i}{2N}$:
$\Rightarrow \E(X_{t+1} | X_t=i) = n \cdot p = i$
\item Martingal-Eigenschaft: $\E(X_{t+1} | X_t) = X_t$
\end{itemize}
\begin{overprint}
\onslide<1>
\vspace{-.5cm}
\begin{align*}
\E(X_t) &= \E(\E(X_{t+1} | X_t)) = \sum_{i=0}^{2N} E(X_{t+1} | X_t = i) \cdot P(X_t = i) \\
&= \sum_{i=0}^{2N} \left( \sum_{j=0}^{2N} j \cdot P(X_{t+1}=j | X_t = i) \right) \cdot P(X_t = i) \\
&= \sum_{j=0}^{2N} j \cdot \left( \sum_{i=0}^{2N} \cdot P(X_{t+1}=j , X_t = i) \right) \\
&= \sum_{j=0}^{2N} j \cdot P(X_{t+1}=j) = \E(X_{t+1})
\end{align*}
\onslide<2>
\begin{equation*}
\Rightarrow \E(X_0) = \E(X_1) = \E(X_2) = \ldots
\end{equation*}
\end{overprint}
\end{frame}
\end{document}

-
Ah, thank you very much. That does the trick for me :-) – Dave Nov 16 '11 at 8:43

Here is another alternative that provide no "wobble" in the transition from one slide to the next.

Instead of using the overprint environment, individual elements are made visible/not by using a combination of \only and \visible overlay specifications. For optimal vertical alignment between the two slides, \vphantom supplied the appropriate vertical spacing in the first line of align* (due to the summation).

\documentclass[xcolor=dvipsnames]{beamer}
\mode<presentation>

\usepackage[ngerman]{babel}
\usepackage[utf8]{inputenc}
\usepackage{lmodern,amsfonts,amsmath,amssymb,amsthm}

\DeclareMathOperator{\Var}{Var}
\DeclareMathOperator{\E}{\mathbb E}

\title{Dummy-Titel}
\subtitle{Dummy-Untertitel}
\author{Autor}

\date{\today}

\begin{document}

\begin{frame}{Erwartungswert}
\begin{itemize}
\item $\E(X_{t+1} | X_t = i) = \sum_{j=0}^{2N} j \cdot P(X_{t+1}=j | X_t = i)$
\item $X_{t+1}$ binomialverteilt mit Parametern $n=2N$ und $p=\frac{i}{2N}$:
$\Rightarrow \E(X_{t+1} | X_t=i) = n \cdot p = i$
\item Martingal-Eigenschaft: $\E(X_{t+1} | X_t) = X_t$
\end{itemize}%
\begin{align*}
\visible<1>{\E(X_t)}
&\only<1>{= \E(\E(X_{t+1} | X_t)) = \sum_{i=0}^{2N} E(X_{t+1} | X_t = i) \cdot P(X_t = i)}%
\only<2>{\Rightarrow \E(X_0) = \E(X_1) = \E(X_2) = \cdots \vphantom{\sum_{i=0}^{2N}}} \\
&\visible<1>{= \sum_{i=0}^{2N} \left( \sum_{j=0}^{2N} j \cdot P(X_{t+1}=j | X_t = i) \right) \cdot P(X_t = i)} \\
&\visible<1>{= \sum_{j=0}^{2N} j \cdot \left( \sum_{i=0}^{2N} \cdot P(X_{t+1}=j , X_t = i) \right)} \\
&\visible<1>{= \sum_{j=0}^{2N} j \cdot P(X_{t+1}=j) = \E(X_{t+1})}
\end{align*}
\end{frame}
\end{document}


The overprint environment itself may have left some gap in addition to what the align* environment would have left above it, causing your items to be shifted down so low. Additionally, the lmodern fonts supported some fonts that were missing from your original MWE.

-
That's a very neat trick. Thanks, I'll keep it at the back of my mind. Also thanks for the hint regarding the fonts. I haven't seen the Latex warning. – Dave Nov 16 '11 at 11:30