How to define a unique height of subscript and superscript indices?

Question

Is there any package that fixes the height of tensor indices?

For example, I'd like to horizontally align indices in the following expression representing antisymmetrization of a and b,

\documentclass{article}
\linespread{1.5}\selectfont
\begin{document}
$e_i^{[a}q^{b]c}$
\end{document}

Is there any universal method not forcing me to use \phantom in each expression, like here?

\documentclass{article}
\linespread{1.5}\selectfont
\begin{document}
$e_i^{[a}q^{b]c}_{\phantom{d}}$
\end{document}

You can give a look at Subscripts for primed variables. (Not an exact duplicate but the problem is basically the same.) — campa, Apr 15 '19 at 07:44
@Sebastiano Thank you, however the tensor package is not working in this case. — Bilbo, Apr 15 '19 at 08:10
@campa I've already provided a better solution above. I'm asking for a package that is positioning all the indices in all the expressions at once. — Bilbo, Apr 15 '19 at 08:12

score 5 · Accepted Answer · answered Apr 15 '19 at 08:12

You could either put a \mathstrut (a box with the height of the ( symbol) into the subscript of q

\documentclass{article}
\linespread{1.5}\selectfont
\begin{document}
$e_i^{[a}q_{\mathstrut}^{b]c}$
\end{document}

or you could adjust the superscript raise and subscript drop document wide

\documentclass{article}
\linespread{1.5}\selectfont
\everymath{
    \fontdimen14\textfont2=1.1ex
    \fontdimen17\textfont2=0.9ex
}
\begin{document}
$e_i^{[a}q^{b]c}$
\end{document}

The second answer is the solution to my question. Thank you! — Bilbo, Apr 15 '19 at 08:22

score 2 · Answer 2 · answered Apr 15 '19 at 11:21

Here's an implementation similar to what the tensor package does, but ensuring empty superscript or subscript is added at each stage.

\documentclass{article}
\usepackage{amsmath,xparse}

\ExplSyntaxOn
\NewDocumentCommand{\tensor}{mm}
 {
  #1
  \group_begin:
  \bilbo_tensor:w #2
 }

\cs_new_protected:Npn \bilbo_tensor:w
 {% start the recursion
  \peek_catcode_remove:NTF \c_math_subscript_token
   {
    \bilbo_tensor_sub:n
   }
   {
    \peek_catcode_remove:NTF \c_math_superscript_token
     {
      \bilbo_tensor_sup:n
     }
     {
      \group_end:
     }
   }
 }
\cs_new_protected:Nn \bilbo_tensor_sub:n
 {% typeset the subscript with a phantom superscript
  {}
  \c_math_subscript_token{#1}
  \c_math_superscript_token{\vphantom{d}}
  % look for a superscript
  \bilbo_tensor_sup:w
 }
\cs_new_protected:Nn \bilbo_tensor_sup:n
 {% typeset the superscript with a phantom subscript
  {}
  \c_math_superscript_token{#1}
  \c_math_subscript_token{\vphantom{d}}
  % look for a subscript
  \bilbo_tensor_sup:w
 }
\cs_new_protected:Npn \bilbo_tensor_sup:w
 {% look for a ^
  \peek_catcode_remove:NTF \c_math_superscript_token
   {
    \bilbo_tensor_sup:n
   }
   {% no ^, end
    \group_end:
   }
 }
\cs_new_protected:Npn \bilbo_tensor_sub:w
 {% look for a _
  \peek_catcode_remove:NTF \c_math_subscript_token
   {
    \bilbo_tensor_sub:n
   }
   {% no _, end
    \group_end:
   }
 }

\ExplSyntaxOff

\begin{document}

$\tensor{e}{_i^{[a}}\tensor{q}{^{b]c}}$

\end{document}

How to define a unique height of subscript and superscript indices?

2 Answers2