Nrthugu

I've seen that usually, the d'Alembertian is written using the command Box, however, this displays a square with all sides identical. I would like to write it in this other way:

in which, the right and below sides are bolder, so that resembles more to the Laplacian symbol.

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}

Build a square with thicker lines the same size of square:

documentclass{article}

usepackage{amsmath,amssymb}



makeatletter

newcommand{dalembertian}{mathop{mathpalettedalembertian@relax}}

newcommand{dalembertian@}[2]{%

  begingroup

  sboxz@{$m@th#1square$}%

  dimen0=fontdimen8

    ifx#1displaystyletextfontelse

    ifx#1textstyletextfontelse

    ifx#1scriptstylescriptfontelse

    scriptscriptfontfififi3

  makebox[wdz@]{%

    hbox to htz@{%

      vrule width dimen0

      kern-dimen0

      vbox to htz@{

        hrule height dimen0 width htz@

        vss

        hrule height 2dimen0

      }%

      kern-2.5dimen0

      vrule width 2.5dimen0

    }%

  }%

  endgroup

}

makeatother



begin{document}



$dalembertian = mathop{{}Delta}-partial_0^2$



$scriptstyledalembertian = mathop{{}Delta}-partial_0^2$



$scriptscriptstyledalembertian = mathop{{}Delta}-partial_0^2$



{Large$dalembertian = mathop{{}Delta}-partial_0^2$}



end{document}

Just uses rules. Then, scalerel to make it match the height of Delta.

documentclass{article}

usepackage{stackengine,scalerel}

newcommanddAlaux{%

  Shortstack{rule{12pt}{.6pt}\

    rule{.6pt}{10pt}kern10ptrule{1.4pt}{10pt}\

    rule{12pt}{1.4pt}}%

}

newcommanddAl{%

  setstackgap{S}{0pt}%

  setstackEOL{\}%

  scalerel*{kern1ptdAlauxkern1pt}{Delta}%

}

begin{document}

$dAl = Delta - partial_0^2,quad phidAlphi e^{phidAlphi}$

end{document}

A slightly thicker version, by adjusting the rule dimensions...

documentclass{article}

usepackage{stackengine,scalerel}

newcommanddAlaux{%

  Shortstack{rule{11pt}{.7pt}\

    rule{.7pt}{9pt}kern9ptrule{1.3pt}{9pt}\

    rule{11pt}{1.35pt}}%

}

newcommanddAl{%

  setstackgap{S}{0pt}%

  setstackEOL{\}%

  scalerel*{kern1ptdAlauxkern1pt}{Delta}%

}

begin{document}

$dAl = Delta - partial_0^2,quad phidAlphi e^{phidAlphi}$

end{document}

Here's a version using scalebox and overlapping three copies of square so that the thickness can be tweaked. The thickness can be changed by increasing or reducing the second argument to add@dalemb.

For instance, with 03 and 06:

and with 05 and 10:

Thicker than this, another add@dalemb would be needed to avoid white spaces between the squares.

documentclass[a4paper,12pt]{article}



usepackage{amssymb}

usepackage{graphicx}



makeatletter

DeclareRobustCommanddalemb{mathpaletteinner@dalemb{}}

definner@dalemb#1{%

  add@dalemb#1{03}%

  add@dalemb#1{06}%

  square

}

defadd@dalemb#1#2{%

  sbox0{scalebox{1.#2}{$#1square$}}%

  rlap{lower0.#2ht0box0}%

}

makeatother



begin{document}



[ Deltadalemb ]

[ partial^{Deltadalemb} ]

[ partial^{partial^{Deltadalemb}} ]



end{document}