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I use hyperlinks in math mode to if a reader does not read my thesis sequentially and finds a very arcane symbol somewhere, he may just click it and go to where it is defined. However, adding links changes the kerning making subscripts and superscripts more spaced out and other ugly things.

Consider this MWE:

\documentclass{article}

\usepackage{amsmath, amssymb, fontspec, unicode-math, tikz}
\usepackage[colorlinks=true, linkcolor=black]{hyperref}

\begin{document}

Let \hypertarget{a}{$X\colon[0,1]\times\Omega\to\mathbb{R}$} be a stochastic
process.

\tikz[overlay, baseline, anchor=base west, inner sep=0, blue]
  \node {${X}_t$};%
\tikz[overlay, baseline, anchor=base west, inner sep=0, red, opacity=0.5]
  \node {$\hyperlink{a}{X}_t$};

\end{document}

The output is bad kerning

I'm using LuaLaTeX and texlive 2013. Is there any way to correct the kerning?

Dimas
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  • Try not to put the \hyperlink in math mode: \hyperlink{a}{${X}_t$}. – Pedro Nov 01 '13 at 14:42
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    The thing is that most times I want the hyperlink in the middle of a complicated equation with a bunch of symbols. More than one symbol can have links and some will point to different targets. – Dimas Nov 01 '13 at 15:44
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    If you define a command \newcommand{\mathhyper}[2]{\text{\hyperlink{#1}{$#2$}}}, you can use it inside equation environments as \mathhyper{a}{X_t}. – Pedro Nov 01 '13 at 15:58
  • It still gives the bad kerning. I think I'll just put the subscript inside the link. – Dimas Nov 01 '13 at 16:12
  • Do you know if there is a constant amount of space inserted after the hyperlink, or if it varies depending on what follows? I have to sort some packages out (no tikz on this system) before I can experiment,but I'm wondering if a constant negative space could be used. – Chris H Nov 01 '13 at 16:19
  • In answer to my own comment - if this seems to be specific to hyperlinks followed by subscripts, even superscripts are as normal (on my system) – Chris H Nov 01 '13 at 16:38
  • So as a workaround \newcommand\hypersub[2]{\hyperlink{#1}{#2}\hspace{-.08em}} defines a hyperlink for use preceding a subscript. My knowledge is nowhere near sufficient to propose a true answer dealing with the general case. – Chris H Nov 01 '13 at 16:43
  • Here is a version that uses the mathhyper command mentioned above. I don't see the kerning problem here - is this similar to what you have tried? – Pedro Nov 01 '13 at 16:56
  • @pedro, mathhyper does not solve it, what solves is putting the subscript inside the hyperlink. \mathhyper{X}_t has the same issues. – Dimas Nov 01 '13 at 19:17
  • @chris-h, I think I saw this on other cases but I can't reproduce them anymore. I only have problems with the subscript, though, and your solution seems adequate. Do you want to post it as an answer? – Dimas Nov 01 '13 at 19:20
  • @Dimas I have done now, but have edited it having found a much better way of doing it, which generalises the solution. – Chris H Nov 04 '13 at 10:18

2 Answers2

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The explanation is the the text of a hyperlink has to be surrounded by \special commands. These are technically called "whatsits". These essentially force TeX to wrap up its processing of the text. In math mode, this includes appending an italic correction. Since the hyperlink text is a math italic X, the italic correction is nonzero. You get the same shifting of the subscript if you put any other whatsit between The X and its subscript. Examples are \write commands and color changes. Try, for example, $X\write16{test}_t$ or $\color{red}X\color{black}_t.

Dan
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  • Just out of curiosity, do you know if a \latelua command is also a whatsit node? – Dimas Nov 04 '13 at 16:48
  • @Dimas I'm afraid LuaTeX is far outside of my expertise; I don't know what \latelua does. But, generally, if some feature requires precise positioning in the page before or after shipout, then a whatsit (or whatsit-like) node is produced, at least for non-luatex engines. – Dan Nov 06 '13 at 19:30
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Edit A real solution uses this answer:

\documentclass{article}
\usepackage{amsmath, amssymb, tikz}
\usepackage[colorlinks=true, linkcolor=black]{hyperref}

\newcommand\hypersub[2]{\hyperlink{#1}{\vphantom{#2}\smash{#2_{}\kern-\scriptspace}}}

\begin{document}
\tikz[overlay, baseline, anchor=base west, inner sep=0, blue]
  \node {${X}_t$};%
\tikz[overlay, baseline, anchor=base west, inner sep=0, red, opacity=0.5]
  \node {$\hypersub{a}{X}_t$};
\end{document}

end edit

This is only a workaround for use when you want to link the primary term excluding the subscript. Defining a specific hyperlink for when a subscript follows as:

\newcommand\hypersub[2]{\hyperlink{#1}{#2}\hspace{-.08em}}

allows:

\tikz[overlay, baseline, anchor=base west, inner sep=0, blue]
  \node {${X}_t$};%
\tikz[overlay, baseline, anchor=base west, inner sep=0, red, opacity=0.5]
  \node {$\hypersub{a}{X}_t$};

to produce:

enter image description here

The mismatch is around 2% of the stroke width of the t.

Community
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Chris H
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