Recentering \bar over to account for integral alignment

Question

I'm trying to write an integral with upper and lower bounds denoted with over- and under-bars respectively. The issue is that because the integral is slanted, it makes it hard to line up the symbols correctly. \underaccent works beautifully (maybe accidentally) to line up the letter and the bar, but \bar puts the accent too far to the left. See below

    \documentclass{beamer}
    \usepackage{amsmath}
    \usepackage{accents}
    \begin{document}
    \begin{frame}{My Integral}
    \[
    \int_{\underaccent{\bar}{c}}^{\bar{ c}} x(c_j) dF(c_j)
    \]   
    \end{frame}
    \end{document}

It seems like there should be a way to move the bar over... but my attempts to recenter the bar using added white space were foiled by math mode's removal of spaces. I'd love to hear your thoughts.

Answer 1

The sansmathaccent package (which in a modern distribution is already loaded by default by beamer) corrects the default bad placement of math accents for sans-serif letters, see Bad positioning of math accents for the beamer standard font. However, the accents package re-implements the math accents, thus destroying the effect of sansmathaccent; in order to avoid this, the accents package can be loaded with the single option. To try and correct the effect of \underaccent one may insert some kerning, such that accents does not try to shift the \bar in the "correct" (from its point of view) position:

\documentclass{beamer}

\usepackage{amsmath}
\usepackage[single]{accents}
\newcommand*{\ubar}[2][0.5]{\underaccent{\bar}{\mkern-#1mu #2 \mkern#1mu}} % optional argument for fine tuning
% \usepackage{sansmathaccent} % shouldn't be necessary nowadays

\begin{document}
\begin{frame}{Accents}
\[
\bar{c} \quad \ubar{c} \quad \int_{\ubar{c}}^{\bar{c}} x(c_j)\,dF(c_j)
\]
\end{frame}
\end{document}

Answer 2

I'm not sure what the notation should mean.

Anyway, there are much simpler examples to see that this does not depend on the integral sign.

\documentclass{beamer}
\usepackage{amsmath}
\usepackage{accents}

\begin{document}

\begin{frame}
\[
\bar{c}+\underaccent{\bar}{c}
\]
\end{frame}

\end{document}

Compare with

\documentclass{article}
\usepackage{amsmath}
\usepackage{accents}

\begin{document}

\[
\bar{c}+\underaccent{\bar}{c}
\]

\end{document}

The fact is that the font used for letters in math mode is not tailored for being used in math, so the internal mechanism fails to properly move the \bar over the characters.

You get better results with arev:

\documentclass{beamer}
\usepackage{amsmath}
\usepackage{accents}
\usepackage{arev,arevmath}

\begin{document}

\begin{frame}
\[
\bar{c}+\underaccent{\bar}{c}
\]   
\end{frame}

\end{document}

If you're very fussy about the placement, you can use, also in your code, \skew:

\documentclass{beamer}
\usepackage{amsmath}
\usepackage{accents}
\usepackage{arev,arevmath}

\begin{document}

\begin{frame}
\[
\skew{2}\bar{c}+\underaccent{\bar}{c}
\]
\end{frame}

\end{document}

Your original example:

\documentclass{beamer}
\usepackage{amsmath}
\usepackage{accents}

\begin{document}

\begin{frame}
\[
\int_{\underaccent{\bar}{c}}^{\skew{3}\bar{c}}x(c_j)\,dF(c_j)
\]   
\end{frame}

\end{document}

(don't forget the thin space in front of the differential).

Answer 3

Quick and dirty:

\documentclass{beamer}
\usepackage{amsmath}
\usepackage{accents}
\newcommand{\mybar}[1]{\bar{#1\hphantom{\:}}\mkern-4mu}
\begin{document}
\begin{frame}{Accents}
\[
\int_{\underaccent{\bar}{c}}^{\mybar{c}} x(c_j)\,dF(c_j)
\]
\end{frame}
\end{document}