# Why is underaccent symbol not centered?

Here's a MWE showing my issue:

\documentclass[11pt,letterpaper,twoside]{book}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{microtype}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{mathtools}
\usepackage{tensor}
\usepackage{accents}

\begin{document}

TEST
$$A = e_{\underaccent{\dot}{0}}^0 \: e_0^{\dot{0}} \: \tensor{T}{^{\dot{0}}_{\underaccent{\dot}{0}}}.$$

\end{document}


Preview:

As you can see on the picture above, the under dot isn't well placed relative to its 0 symbol, while it is the case for the upper dot. Why? How can I solve this centering issue?

This centering issue is more obvious when using "1" instead of "0".

• It occurs because it is expecting the accent to occur on an italic glyph that possesses a measure of slant (numerals possess no slant). Not sure how to fix without using an alternate approach, such as \underset{\dot{}}{0}. May 5, 2020 at 18:30
• Apparently, adding \mathrm around it solves the issue.
– Cham
May 5, 2020 at 18:35
• Very nice "fix"! May 5, 2020 at 18:40
• You should consider answering your own question. I would give it an upvote. May 5, 2020 at 19:09

Here's a possible fix, using the command \mathrm :

\documentclass[11pt,letterpaper,twoside]{book}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{microtype}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{mathtools}
\usepackage{tensor}
\usepackage{accents}

\begin{document}

TEST
$$A = e_{\mathrm{\underaccent{\dot}{0}}}^0 \: e_0^{\dot{0}} \: \tensor{T}{^{\dot{0}}_{\mathrm{\underaccent{\dot}{0}}}}.$$

\end{document}


Maybe there's a better method in writing a small accent under a math symbol?

In the modern toolchain with unicode-math, you can declare the Unicode combining dot-below accent with \DeclareUnicodeAccent, although it is only usable in text mode:

\documentclass[11pt,letterpaper,twoside]{book}
\usepackage{mathtools}
\usepackage{unicode-math}
\usepackage{microtype}

\DeclareUnicodeAccent{\dotbelow}{TU}{"0323}
\newcommand\zerodot{\mathord{\text{\normalfont\dotbelow{0}}}}

\begin{document}

$A = e_{\zerodot}^0 \: e_0^{\dot{0}} \: T^{\dot{0}}_{\zerodot}.$

\end{document}


Unfortunately, this is not compatible with tensor. You might try tensind instead.