[Tex/LaTex] Unusual symbol in equation

equationssymbols

How can I type the following in LaTeX?

Enter image description here

Best Answer

I guess the main issues are, how to create a large open square symbol, center it on the math axis, and have it act as a math operator, i.e., place its argument below (and above, if there's an upper limit) the large open square. Sort of like \sum, right? A series of \vcenter, \hbox, and repeated \mathlarger instructions applied to the \Box macro solve these issues. (If you compare the following screenshot with the preceding one, you'll notice that the letter g to the left of the box is placed ever so slightly higher now.)

enter image description here

\documentclass{article}
\usepackage{amsmath,  % for "\DeclareMathOperator*" macro
            amsfonts, % for "\Box" macro
            relsize}  % for "\mathlarger" macro
\newcommand{\BigBox}{\vcenter{\hbox{$\mathlarger{\mathlarger 
     {\mathlarger{\mathlarger{\mathlarger{\Box}}}}}$}}}
\DeclareMathOperator*{\bigsquare}{\BigBox}

\begin{document}
\[
Z_{\mathcal{T}/G}\equiv \sum_{h\in G}\frac{1}{|G|} 
     \sum_{g\in G} g {\bigsquare_{\textstyle h}}
\]
\end{document}

Addendum -- Another way to create \BigBox is to load the graphicx package and to run

\newcommand{\BigBox}{\vcenter{\hbox{\scalebox{2}{$\Box$}}}}

As you've indicated in a comment that \BigBox isn't an "operator" but a partition function with boundary conditions, I think it makes sense -- from a LaTeX point of view -- to define a macro called, say \partfunc, that takes two arguments, here: g and h, and to align the first argument on the math axis.

enter image description here

\documentclass{article}
\usepackage{amsmath,  % for "\DeclareMathOperator*" macro
            amsfonts, % for "\Box" macro
            graphicx} % for "\scalebox" macro
\newcommand\BigBox{\vcenter{\hbox{\scalebox{2}{$\Box$}}}}
\newcommand\bigsquare{\mathop{\BigBox}\limits}
\newcommand\partfunc[2]{\vcenter{\hbox{$\textstyle #1$}}{\bigsquare_{\textstyle #2}}}

\begin{document}
\[
Z_{\mathcal{T}/G}\equiv \sum_{h\in G}\frac{1}{|G|} 
     \sum_{g\in G} \partfunc{g}{h}
\]
\end{document}
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