[Tex/LaTex] Subscript vertical position dependent on presence of superscript – how to change?

subscriptssuperscriptsvertical alignment

Possible Duplicate:
Subscripts for primed variables

If I have a variable which is always subscripted but only sometimes superscripted, the vertical position of the subscript varies. For instance, $s^*_i$ and $s^{}_i$ are different from $s_i$. Can I define the subscript such that it is always in the same position regardless of the presence of a superscript?

Best Answer

\usepackage{subdepth}

Example

\documentclass{article}
\usepackage{subdepth}
\begin{document}
$a_i a_i^2$
\end{document}

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