How to control the vertical space below a double-underline?

Question

I use an edited version of the \\uline command from the ulem package to get a nice compact double underline to denote tensor variables. The used code comes from this question. My problem is that the macro leaves a very large space below any line with a tensor. I would like this vertical space to be the same as for a simply underlined letter, or even the same as for a standard letter without underlines. How would I do that?

Full example:

\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage[normalem]{ulem}
\makeatletter
\renewcommand*{\uuline}{%
  \bgroup
  \UL@setULdepth
  \markoverwith{%
    \lower\ULdepth\hbox{%
      \kern-.03em%
      \vtop{%
        \hrule width.2em%
        \kern 0.6pt % distance between the two underlines
        \hrule
      }%
      \kern-.03em%
    }%
  }%
  \ULon
}
\makeatother
\setlength{\ULdepth}{1pt}  % distance from double underline to letter
\newcommand{\mat}[1]{\uuline{#1}{}}

\begin{document}
This is some text with $\mat A$ in it. The problem is that the next line of
text leaves a very big vertical space. The same problem occurs in displayed
maths:

\begin{align*}
A & = B \\
\mat A & = \mat B \\
A & = B
\end{align*}

\end{document}

Double underline for tensors is very old-fashioned, isn't it? — egreg, Feb 13 '19 at 10:56

score 2 · Accepted Answer · answered Feb 13 '19 at 10:30

2

You can \smash the underline, i.e., set the height and the depth of the box around the underlined letter to 0.

Code:

\newcommand{\mat}[1]{\smash{\uuline{#1}{}}}

Result:

answered Feb 13 '19 at 10:30

Marijn

37,699

This is like sweeping dirt under the rug. – egreg Feb 13 '19 at 11:14

score 1 · Answer 2 · answered Feb 13 '19 at 11:12

I wouldn't use ulem for this, but use \underline, with some tricks for decreasing the clearance between the two lines. This does not completely eliminate the risk of getting more interline space, but should reduce it to the minimum.

To be honest, I would not use double underlining at all; the modern conventions used in technical fields say that tensors should be denoted by slanted sans serif letters.

\documentclass{article}
\usepackage{amsmath}

\makeatletter
\newcommand{\mat}[1]{{\mathpalette\mat@{#1}}}
\newcommand{\mat@}[2]{%
  \begingroup
  \sbox\z@{$\m@th#1\underline{#2}$}%
  \dimen@=\dp\z@ \advance\dimen@ -2\mat@dimen{#1}%
  \dp\z@=\dimen@
  \sbox\z@{$\m@th\underline{\box\z@}$}%
  \box\z@
  \endgroup
}
\newcommand\mat@dimen[1]{%
  \fontdimen8
  \ifx#1\displaystyle\textfont\else
  \ifx#1\textstyle\textfont\else
  \ifx#1\scriptstyle\scriptfont\else
  \scriptscriptfont\fi\fi\fi 3
}
\makeatother

\begin{document}
This is some text with $\mat{A}$ in it. The problem is that the next line of
text leaves a very big vertical space. The same problem occurs in displayed
maths:
\begin{align*}
A & = B \\
\mat{A} & = \mat{B} + x_{\mat{C}}\\
A & = B + \mat{C}
\end{align*}

\end{document}

Bilal Yilmaz · Answer 3 · 2023-07-01T10:31:49.120

0

Try this:

\raisebox{-0.5mm}{\underline{\raisebox{0.5mm}[1mm][1mm]{\underline{$\dfrac{1}{2}$}}}}

edited Jul 01 '23 at 10:31

answered Jul 01 '23 at 10:19

Bilal Yilmaz

315

How to control the vertical space below a double-underline?

3 Answers3

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