[Tex/LaTex] Fractions in superscripts are placed too low

math-modepositioningsuperscripts

I have noticed that "tall" superscripts seem to be placed awkwardly low in math mode; their baseline is so close to the main baseline that confusion has happened.

\documentclass{article}
\begin{document}\centering
  \( 2^{\left\lfloor\frac{1}{2}\right\rfloor} \quad 2^a \quad 
     2^{\left\lfloor\frac{1}{2}\right\rfloor}_{\phantom{i}} 
  \)
  \[ 2^{\left\lfloor\frac{1}{2}\right\rfloor} \quad 2^a \quad 
     2^{\left\lfloor\frac{1}{2}\right\rfloor}_{\phantom{i}} 
  \]
\end{document}

With texlive 2012, this code compiles to this:

enter image description here

There does not seem to be a significant difference between text and display mode. Including a phantom subscript raises the exponent up to (roughly?) the usual baseline; this is fine for the purpose of clarity, but I'll admit it looks kind of awkward. Also, treating all instances thus is not feasible.

How can I ensure that "tall" superscripts are clearly identifiable as such?

Best Answer

enter image description here

See appendix G of the TeXbook for full details about the font parameters of the symbol font control script positions.

\documentclass{article}

\begin{document}\centering

  \( 2^{\left\lfloor\frac{1}{2}\right\rfloor} \quad 2^a \quad 
     2^{\left\lfloor\frac{1}{2}\right\rfloor}_{\phantom{i}} 
  \)
  \[ 2^{\left\lfloor\frac{1}{2}\right\rfloor} \quad 2^a \quad 
     2^{\left\lfloor\frac{1}{2}\right\rfloor}_{\phantom{i}} 
  \]

\setbox0\vbox{\hbox{$$}$$ $$}
\fontdimen13\textfont2 = 10pt
\fontdimen14\textfont2 = 7pt
  \( 2^{\left\lfloor\frac{1}{2}\right\rfloor} \quad 2^a \quad 
     2^{\left\lfloor\frac{1}{2}\right\rfloor}_{\phantom{i}} 
  \)
  \[ 2^{\left\lfloor\frac{1}{2}\right\rfloor} \quad 2^a \quad 
     2^{\left\lfloor\frac{1}{2}\right\rfloor}_{\phantom{i}} 
  \]
\end{document}

If you don't want to mess with fontdimens (which isn't as bad as it seems, although I was using extreme values to highlight the effect) you could move the subscript so it has no depth which will change TeX's positioning logic for example

\def\bigsup#1{^{\vbox{\hbox{$\scriptstyle#1$}\nointerlineskip\hbox{}}}}


  \( 2\bigsup{\left\lfloor\frac{1}{2}\right\rfloor} \)

produces

enter image description here

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