[Tex/LaTex] 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}

Answer 1

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: