Typesetting d'Alembertian symbol
Build a square with thicker lines the same size of \square
:
\documentclass{article}
\usepackage{amsmath,amssymb}
\makeatletter
\newcommand{\dalembertian}{\mathop{\mathpalette\dalembertian@\relax}}
\newcommand{\dalembertian@}[2]{%
\begingroup
\sbox\z@{$\m@th#1\square$}%
\dimen0=\fontdimen8
\ifx#1\displaystyle\textfont\else
\ifx#1\textstyle\textfont\else
\ifx#1\scriptstyle\scriptfont\else
\scriptscriptfont\fi\fi\fi3
\makebox[\wd\z@]{%
\hbox to \ht\z@{%
\vrule width \dimen0
\kern-\dimen0
\vbox to \ht\z@{
\hrule height \dimen0 width \ht\z@
\vss
\hrule height 2\dimen0
}%
\kern-2.5\dimen0
\vrule width 2.5\dimen0
}%
}%
\endgroup
}
\makeatother
\begin{document}
$\dalembertian = \mathop{{}\Delta}-\partial_0^2$
$\scriptstyle\dalembertian = \mathop{{}\Delta}-\partial_0^2$
$\scriptscriptstyle\dalembertian = \mathop{{}\Delta}-\partial_0^2$
{\Large$\dalembertian = \mathop{{}\Delta}-\partial_0^2$}
\end{document}
To increase the boarder on two sides, you could use the \ding{113}
symbol from pifont
\documentclass{article}
\usepackage{pifont}
\usepackage{amsmath}
\begin{document}
$\text{\ding{113}} \Delta$
\end{document}
Just uses \rule
s. Then, \scalerel
to make it match the height of \Delta
.
\documentclass{article}
\usepackage{stackengine,scalerel}
\newcommand\dAlaux{%
\Shortstack{\rule{12pt}{.6pt}\\
\rule{.6pt}{10pt}\kern10pt\rule{1.4pt}{10pt}\\
\rule{12pt}{1.4pt}}%
}
\newcommand\dAl{%
\setstackgap{S}{0pt}%
\setstackEOL{\\}%
\scalerel*{\kern1pt\dAlaux\kern1pt}{\Delta}%
}
\begin{document}
$\dAl = \Delta - \partial_0^2,\quad \phi\dAl\phi e^{\phi\dAl\phi}$
\end{document}
A slightly thicker version, by adjusting the \rule
dimensions...
\documentclass{article}
\usepackage{stackengine,scalerel}
\newcommand\dAlaux{%
\Shortstack{\rule{11pt}{.7pt}\\
\rule{.7pt}{9pt}\kern9pt\rule{1.3pt}{9pt}\\
\rule{11pt}{1.35pt}}%
}
\newcommand\dAl{%
\setstackgap{S}{0pt}%
\setstackEOL{\\}%
\scalerel*{\kern1pt\dAlaux\kern1pt}{\Delta}%
}
\begin{document}
$\dAl = \Delta - \partial_0^2,\quad \phi\dAl\phi e^{\phi\dAl\phi}$
\end{document}