[texhax] Cases for italic correction
Khaled Hosny
khaledhosny at eglug.org
Fri Jul 20 16:43:18 CEST 2012
On Fri, Jul 20, 2012 at 09:48:50AM -0400, Barbara Beeton wrote:
> On Fri, 20 Jul 2012, Philip TAYLOR wrote:
>
> Barbara Beeton wrote:
>
> > unlike all other letters in the cm math italic
> > font, the d has no built-in "overhang" spacing.
> > i've never actually asked, but i think the
> > reason for this is that knuth uses d only for
> > indicating derivatives (as in "dx"), not for
> > variables, and for that use, he prefers it to
> > be directly adjacent to the variable involved,
> > not separated by a small space.
>
> But what of a second derivative ? That would require d^2y/dx^2,
> which will surely generate almost exactly the same inteference
> as Michael asserts obtains in d^3 (but which Lars and I cannot see).
>
> good question. there's not a single one
> in the texbook -- i checked with grep in
> texbook.tex; i also checked for "d{}" and
> "d\/" and several other increasingly
> obscure possibilities ... nothing.
>
> so we have no direct knuthian example.
>
> however, i don't see the difference either;
> here's my test:
>
> \documentclass[12pt]{article}
> \begin{document}
> \Large
> $dx + d^2x + d{}^2x + d\/^2x$
> \end{document}
>
> definitely a puzzlement.
> -- bb
I just checked cmmi10.tfm, there is no italic correction for the d
indeed, so any of those construction wouldn't make any visible
difference.
A better test:
\tracingonline=1
\showboxbreadth=\maxdimen
$d^3 d\/^3 d{}^3$
\showlists
\bye
Which gives:
\teni d
\hbox(4.51111+0.0)x4.48613, shifted -3.62892
.\sevenrm 3
\teni d
\kern0.0
\hbox(4.51111+0.0)x4.48613, shifted -3.62892
.\sevenrm 3
\teni d
\hbox(0.0+0.0)x0.0
\hbox(4.51111+0.0)x4.48613, shifted -3.62892
.\sevenrm 3
So \/ is inserting a zero kern, and {} is inserting a zero width box,
nothing else.
Regards,
Khaled
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