# Misalignment in custom big symbol using mathop

Following the advice of this question, I created the \itsep symbol:

\newcommand{\itsep}{\mathop{\scalebox{1.5}{\raisebox{-0.2ex}{$\circledast$}}}}


When used with single character sub/super-scripts, it displays properly, like this:

a \itsep^f_{g} b


If I place multiple characters in the sub-script the symbol behaves incorrectly:

a \itsep^f_{g \, a \, b} b


Is there a way to make this symbol truly behave like \sum or \bigwedge where the "big" symbol is centered over the subscript and centered under the superscript?

if, instead of using the basic \mathop you use \DeclareMathOperator* from amsmath, this "insulates" the result from its context:

\DeclareMathOperator*{\itsep}{\scalebox{1.5}{\raisebox{-0.2ex}{$\circledast$}}}


thus

$a \itsep^f_{g} b \qquad a \itsep^f_{g \, a \, b} b$


results in

For reference, mathtools provides \mathclap which allows for zero-width centred overlap of math content, based on the size its used in:

\documentclass{article}
\usepackage{mathtools}% http://ctan.org/pkg/mathtools
\usepackage{amssymb}% http://ctan.org/pkg/amssymb
\usepackage{graphicx}% http://ctan.org/pkg/graphicx
\begin{document}
\newcommand{\itsep}{\mathop{\scalebox{1.5}{\raisebox{-0.2ex}{$\circledast$}}}}
$a \itsep^f_{g} b \qquad a \itsep^f_{g \, a \, b} b \qquad a \itsep^f_{\mathclap{g \, a \, b}} b$
\end{document}​


It depends on your use case whether this would be a problem when having excessively long subscripts, which may extend into the horizontal domain of the "operands" a and b.

• I've used \mathclap before and it certainly is an interesting solution to this problem (that I hadn't thought of), but it is my preference to simply make the symbol behave like other "big" symbols and only have to present a fix at the definition rather than fixing it at each instance as this mathclap solution does. – Arlen Cox Aug 2 '12 at 22:01