Highlighting equation with text below using hf-tikz - \endcsname error

Question

I am trying to highlight one variable in an equation with annotation using Beamer (with help of automatic space adjustments following this suggestion Text below equation with hf-tikz). The slide contains an itemize environment with explanatory notes as well. Here a minimum working example for Beamer.

\documentclass{beamer}
\usefonttheme{professionalfonts}
\usefonttheme{serif}
\usefonttheme{structuresmallcapsserif}
\usepackage{amsmath, amssymb}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\usepackage[beamer,markings]{hf-tikz}
\usepackage{mathtools,xparse} % texted arrows

\newcommand<>{\annotate}[2][]{
\onslide#3{
    \tikz[remember picture,overlay]\node[#1,use marker id] at (0,0){#2};
}
}

\newlength{\notewidth}
\newcommand{\setnotewidth}[1]{%
\settowidth{\notewidth}{$#1$}%
}

\newcommand{\mth}[2]{
\setnotewidth{#2}
\mathmakebox[0.100\notewidth]{#1}
}

\NewDocumentCommand{\tikzmarkaligned}{r<> o m m}{
\phantom{\mth{#3}{#4}}
\tikzmarkin<#1>[#2]{#3}#3\tikzmarkend{#3}
\phantom{\mth{#3}{#4}}
}

\def\savepointas#1#2{%
\expandafter\gdef\csname save@pt@#1\endcsname{#2}%
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

    \newcommand\indentdisplays[1]{%
\everydisplay{\addtolength\displayindent{#1}%
    \addtolength\displaywidth{-#1}}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\setbeamertemplate{footline}[frame number]
\setbeamertemplate{navigation symbols}{}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{document}
\begin{frame}
\transwipe
\begin{itemize}

\item<1->[]{ \indentdisplays{-3em}  \begin{equation} \mathbf{pb_{i,\,t}} = \underbrace{\gamma_{i}~\{~+\delta_{t}\}}_{\textrm{fixed effects}} + \alpha \cdot pb_{i,\,t-1} + 
\tikzmarkaligned<1->[mark at=0.825]{\beta_{0 (t)}}{\beta_{0\,(t)} \gg 0}
\annotate<1->[below,black,font=\scriptsize]{$\beta_{0\,(t)} \gg 0$}~\cdot~d_{i,\,t-1} \mathbf{\vartheta_{i,\,t}},   \end{equation} }

\begin{itemize}
\item<1->{$ pb_{i,\,t} = \tau_{i,\,t} - g_{i,\,t} - ir_{i,\,t}$}

\item<2->{}
\item<2->[]{ \setbeamercolor{postit}{fg=black,bg=gray!10} \begin{beamercolorbox}[\vskip -1.35em,\hskip 0.0em,wd=\linewidth,rounded=true,shadow=true]{postit} {\textbf{\emph{Sufficient}} but not necessary condition} \end{beamercolorbox}}

\end{itemize}
\end{itemize}
\end{frame}
\end{document}

It works with error message

Missing \endcsname inserted. \end{frame}.

If I use any greek letter and/or expression with \ such as \,, then another error message appears

Missing \endcsname inserted. \savepointas...

Then, the coloured box is not adjusted, a part of the equation is missing.

Since I am now to using tikz, I may be missing a definition of an object. Any suggestion is welcome.

Answer 1

There are two problems here.

• The first one is that beamercolorbox apparently doesn't like to have spacing instructions passed ad options. Those should be placed before the \begin.
• The second one is in the definition of \tikzmarkaligned. I will address it out of this bullet list.

Let us recollect part of the preamble:

\newcommand{\mth}[2]{
\setnotewidth{#2}
\mathmakebox[0.100\notewidth]{#1}
}
\NewDocumentCommand{\tikzmarkaligned}{r<> o m m}{
\phantom{\mth{#3}{#4}}
\tikzmarkin<#1>[#2]{#3}#3\tikzmarkend{#3}
\phantom{\mth{#3}{#4}}
}

Now I don't know exactly what the \tikzmarkin and \tikzmarkend macros do. According to the hf-tikz documentation, they insert the delimiters for the colored region. However, they seem not to like greek letters inside them. So feeding #3 into both is looking for trouble, since #3 is what is supposed to be colored. The best thing, seen as it is #4 that is used to set the width for the coloring while #3 is typeset, would be to feed #4 to those two macros and then fill it with a random foobarbaz type string that causes no trouble and has roughly the correct width, i.e. the same width as #3.

So the code can be amended to:

\documentclass{beamer}
\usefonttheme{professionalfonts}
\usefonttheme{serif}
\usefonttheme{structuresmallcapsserif}
\usepackage{amsmath, amssymb}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage[beamer,markings]{hf-tikz}
\usepackage{mathtools,xparse} % texted arrows
\NewDocumentCommand{\annotate}{r<>O{}m}{
\onslide#1{
    \tikz[remember picture,overlay]\node[#2,use marker id] at (0,0){#3};
}
}
\newlength{\notewidth}
\newcommand{\setnotewidth}[1]{%
\settowidth{\notewidth}{$#1$}%
}
\newcommand{\mth}[2]{
\setnotewidth{#2}
\mathmakebox[0.100\notewidth]{#1}
}
\NewDocumentCommand{\tikzmarkaligned}{r<> o m m}{
\phantom{\mth{#3}{#4}}
\tikzmarkin<#1>[#2]{#4}#3\tikzmarkend{#4}
\phantom{\mth{#3}{#4}}
}
\def\savepointas#1#2{%
\expandafter\gdef\csname save@pt@#1\endcsname{#2}%
}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newcommand\indentdisplays[1]{%

\everydisplay{\addtolength\displayindent{#1}%
    \addtolength\displaywidth{-#1}}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\setbeamertemplate{footline}[frame number]
\setbeamertemplate{navigation symbols}{}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}
\begin{frame}
\transwipe
\begin{itemize}
\item<1->[]{ \indentdisplays{-3em}  \begin{equation} \mathbf{pb_{i,,t}} = \underbrace{\gamma_{i}~{~+\delta_{t}}}{\textrm{fixed effects}} + \alpha \cdot pb{i,,t-1} + 
\tikzmarkaligned<1->[mark at=0.825]{\beta_{0 (t)}}{foobarbaz}
\annotate<1->[below,black,font=\scriptsize]{$\beta_{0,(t)} \gg 0$}~\cdot~d_{i,,t-1} \mathbf{\vartheta_{i,,t}},   \end{equation} }
\begin{itemize}
\item<1->{$ pb_{i,,t} = \tau_{i,,t} - g_{i,,t} - ir_{i,,t}$}
\item<2->{}
\item<2->[]{ \setbeamercolor{postit}{fg=black,bg=gray!10} \vskip -1.35em \hskip 0.0em \begin{beamercolorbox}[wd=\linewidth,rounded=true,shadow=true]{postit} {\textbf{\emph{Sufficient}} but not necessary condition} \end{beamercolorbox}}
\end{itemize}
\end{itemize}
\end{frame}
\end{document}

This compiles fine, and gives:

Unfortunately I am no longer sure this is what was desired, since the comment I posted had a wrong url giving this image instead, which comes from Claudio Fiandrino's answer here, as the code in the OP's MWE.

Note that to adjust the box it is necessary to compile twice.

In a comment above, I stated I had gotten a:

Package pgf error: no marker shape "marker unit vector-1" is known

error. I have no idea where that came from or how to solve it. All I noticed was that eliminating marker id from the definition of \annotate the error vanished.

Update

I saw that something was wrong with the equation. I realized there was an extra 1-. Having changed the definition of \annotate from OP's code to:

\NewDocumentCommand{\annotate}{r<>O{}m}{
\onslide#1{
    \tikz[remember picture,overlay]\node[#2,use marker id] at (0,0){#3}
}
}

produced \onslide1-, which caused \onslide to do nothing, and the 1- to be typeset. My bad. Reverting to:

\newcommand<>{\annotate}[2][]{
\onslide#3{
    \tikz[remember picture,overlay]\node[#1,use marker id] at (0,0){#2};
}
}

fixes this. I don't know why though. I have never seen \newcommand<>. Apparently, this is a trick to define a command taking an argument wrapped in <> as #3 and then parsing what follows as a normal \newcommand would. So \annotate<1->[…]{……} has 1- as #3, … as #1 and …… as #2.

Update on \savepointas

As I said in comments, I think it is plain useless, as it is never invoked in the code. Perhaps it is invoked by some package command used in one of the defined commands. Anyways I tried compiling with and without it. Here is the code:

\documentclass{beamer}
\usefonttheme{professionalfonts}
\usefonttheme{serif}
\usefonttheme{structuresmallcapsserif}
\usepackage{amsmath, amssymb}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage[beamer,markings]{hf-tikz}
\usepackage{mathtools,xparse} % texted arrows
\newcommand<>{\annotate}[2][]{
\onslide#3{
    \tikz[remember picture,overlay]\node[#1,use marker id] at (0,0){#2};
}
}
\newlength{\notewidth}
\newcommand{\setnotewidth}[1]{%
\settowidth{\notewidth}{$#1$}%
}
\newcommand{\mth}[2]{
\setnotewidth{#2}
\mathmakebox[0.100\notewidth]{#1}
}
\NewDocumentCommand{\tikzmarkaligned}{r<> o m m}{
\phantom{\mth{#3}{#4}}
\tikzmarkin<#1>[#2]{#4}#3\tikzmarkend{#4}
\phantom{\mth{#3}{#4}}
}
\def\savepointas#1#2{%
\expandafter\gdef\csname save@pt@#1\endcsname{#2}%
}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\newcommand\indentdisplays[1]{%

\everydisplay{\addtolength\displayindent{#1}%
    \addtolength\displaywidth{-#1}}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\setbeamertemplate{footline}[frame number]
\setbeamertemplate{navigation symbols}{}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}
\begin{frame}
\transwipe
\begin{itemize}
\item<1->[]{ \indentdisplays{-3em}  \begin{equation} \mathbf{pb_{i,,t}} = \underbrace{\gamma_{i}~{~+\delta_{t}}}{\textrm{fixed effects}} + \alpha \cdot pb{i,,t-1} + 
\tikzmarkaligned<1->[mark at=0.825]{\beta_{0 (t)}}{foobarbaz}
\annotate<1->[below,black,font=\scriptsize]{$\beta_{0,(t)} \gg 0$}~\cdot~d_{i,,t-1} \mathbf{\vartheta_{i,,t}},   \end{equation} }
\begin{itemize}
\item<1->{$ pb_{i,,t} = \tau_{i,,t} - g_{i,,t} - ir_{i,,t}$}
\item<2->{}
\item<2->[]{ \setbeamercolor{postit}{fg=black,bg=gray!10} \vskip -1.35em \hskip 0.0em \begin{beamercolorbox}[wd=\linewidth,rounded=true,shadow=true]{postit} {\textbf{\emph{Sufficient}} but not necessary condition} \end{beamercolorbox}}
\end{itemize}
\end{itemize}
\end{frame}
\end{document}

Output with that \def line:

Output without it:

See any difference? I really don't… If you get a different result, you probably have an outdated version of one or more packages.