math-modesubscripts
When I add a subscript to a primed variable, the subscript is rendered lower than when it is a subscript to an unprimed variable.
For example, when I compile
$l_x l'_x l_x l'_x l_x l'_x$
I get
The subscript x is at a different height for the primed variables and the unprimed ones.
Any one have any idea why this is happening? And how I can fix this so that the subscript of the primed variable appears at the same height? (Or am I doing something wrong?)
In this instance you can use \mathstrut as a supplement for the missing \dagger:
\documentclass{article}
\usepackage{xcolor}% http://ctan.org/pkg/xcolor
\begin{document}
\leavevmode\rlap{$c_R c^{\dagger}_R c^{\mathstrut}_R$}%
{\color{black!20}\rule[-1ex]{4em}{.4pt}}
\leavevmode{\color{red}\rlap{$c^{\mathstrut}_R$}}$c^\dagger_R$
\leavevmode{\color{red}\rlap{$c^{}_R$}}$c^\dagger_R$
\end{document}
The horizontal rule in the output is just for reference in the first output.
The second output prints an overlay between the \mathstrut and \dagger superscript versions, while the third output overlays the {} and \dagger superscript versions (using xcolor). The differences is more noticeable this way.
The subscript is lower with \sup than with \inf simply because the letter "p" goes below the baseline. You could change this behavior and define new commands where the subscript of \sup would be higher, or where the subscript of \inf would be lower.
For example,
\documentclass{article}
\usepackage{mathtools}
\newcommand{\newsup}{\mathop{\smash{\mathrm{sup}}}}
\newcommand{\newinf}{\mathop{\mathrm{inf}\vphantom{\mathrm{sup}}}}
\begin{document}
\begin{tabular}{ll}
Default: & \(\displaystyle \sup_{i\in I},\; \inf_{i\in I} \) \\
Raised subscript in \verb|\sup|: & \(\displaystyle \newsup_{i\in I},\; \inf_{i\in I} \) \\
Lowered subscript in \verb|\inf|: & \(\displaystyle \sup_{i\in I},\; \newinf_{i\in I} \) \\
\end{tabular}
\end{document}
However, in both modified cases, it looks weird (at least in my opinion), since the subscript overlaps on the "p" in one case, and there is a lot of white space between \inf and its subscript in the other case. I agree that the default might not be entirely satisfying, but I think it's still the best.
Best Answer
This behaviour is intended, but not always desired. My somewhat neglected
subdepthpackage alters this so the subscript height is constant in these situations. Just load the package.