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This question already has an answer here:

In a document that uses the newtx packages, double subscripts seem to have too much spacing.

\documentclass{scrartcl}
\usepackage{newtxtext}
\usepackage{newtxmath}

\pagestyle{empty}

\begin{document}
  $\lambda_{\alpha_p}$
\end{document}

Double subscript with txfonts

The spacing with the default font looks much better:

Double subscript with default font

It also happens with newtx if Latin letters are used:

Double subscript with Latin letters

More pairs tested:

Pairs

Is there anything I can do at the "user" level (short of inserting \! all over the place) to fix this?

Related, but not the same: newtxmath subscript spacing too large.

marked as duplicate by Mico math-mode Aug 25 '15 at 13:50

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • If you think that certain character pairings look wrong, you should inform the designer of that font or the maintainer of that package. Maybe they can fix the kerning. – LaRiFaRi Aug 25 '15 at 9:48
  • @LaRiFaRi: I've sent a message to Michael Sharpe, the author and maintainer of newtxmath. – krlmlr Aug 25 '15 at 10:48
  • Ideally, the newtxmath package would offer an option called subscriptcorrection, similar to the one already offered by the mtpro2 package. (My answer -- see below -- shows how to use the mtpro2 package with the subscriptcorrection option.) See this answer by @egreg for the code that implements the subscript correction for any math font package. Good news: As newtxmath and mtpro2 are both Times Roman math clones, you should be able to use Enrico's code "out of the box", i.e., without needing to modify any of the spacing corrections. – Mico Aug 25 '15 at 13:35
2

No guarantee! Might effect parts of your document which you do not want to change.

% arara: pdflatex

\documentclass{scrartcl}
\usepackage{newtxtext}
\usepackage{newtxmath}
\catcode`_=\active
\newcommand_[1]{\sb{\mspace{-1.5mu}#1}}

\pagestyle{empty}

\begin{document}
    $\lambda_{\alpha_p}$

    $l_{\alpha_p}$
\end{document}

enter image description here

  • Is it just me, or is the spacing before $p$ still too wide? – krlmlr Aug 25 '15 at 10:06
  • @krlmlr For a instead of \alpha it looks better. That is a problem of kerning from the font design. If you have some single pairings you do not like, just define something like \newcommand*{\subp}{_{\mspace{-2.5mu}p}} (not tested) or alike. – LaRiFaRi Aug 25 '15 at 10:20
  • Can I fix the kerning myself, so that perhaps I can later show my findings to the font designer/package author? – krlmlr Aug 25 '15 at 10:35
  • @krlmlr I guess you can: tex.stackexchange.com/q/10455. But this will be some work. – LaRiFaRi Aug 25 '15 at 10:37
  • Enrico has shown how to adapt the subscriptcorrection option of the mtpro2 package to any math font package. – Mico Aug 25 '15 at 13:39
1

For this math font and combination of letters, I think you need to insert a negative thinspace, \!, i.e., write \alpha_{\!p} instead of just \alpha_!p. This applies to cases where \alpha is on the baseline or in the first subscript position.

The following screenshot shows the letter combinations with this adjustment on the left, and without the adjustment on the right.

Note that, depending on the font in use, there will always be some combinations of letters for which manual spacing adjustments are needed in math mode in order to achieve the optimal typographic look.

enter image description here

\documentclass{scrartcl}
\usepackage{newtxtext,newtxmath}
\begin{document}
$\alpha_{\!p}$           $\alpha_p$

$\lambda_{\alpha_{\!p}}$ $\lambda_{\alpha_p}$
\end{document}

Addendum: If you choose to work with the MathTime Professional II math font package instead of the newtxmath package, you can get the subscript positioning correction automatically by specifying the option subscriptcorrection. (Both mtpro2 and newtxmath are Times Roman Math fonts.) Note that whereas the full mtpro2 package is not free of charge, its "lite" subset -- which is all that's needed for this example -- is in fact free of charge. Observe in the screenshot below that hardly any difference is visible between the version with the explicit \! correction on the left and the automatic correction on the right. (Well, there's a tiny difference, as my manual correction amounts to \mkern-3mu, whereas the automatic one by the mtpro2 package amounts to \mkern-2mu.)

enter image description here

\documentclass{article}
\usepackage{newtxtext}
\usepackage[lite,subscriptcorrection]{mtpro2}
\pagestyle{empty}
\begin{document}
$\alpha_{\!p}$           $\alpha_p$

$\lambda_{\alpha_{\!p}}$ $\lambda_{\alpha_p}$
\end{document}

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