[luatex] Poor Spacing in the \frac Environment

[Reinhard Kotucha]

On 2015-01-19 at 15:51:15 -0600, Dan Luecking wrote:

 > On 2013-01-18 at 21:59:19 CET, Reinhard Kotucha wrote
 > 
 > >On 2015-01-18 at 23:52:39 -0500, Emil E wrote:
 > >
 > >  > I've also noted that LuaLaTeX is making the correct adjustments for
 > >  > superscripted denominators (ex. a denominator of \delta^{2}), but
 > >  > this _only_ occurs on the LuaLaTeX engine with OTF TeX Gyre Pagella
 > >  > fonts (it does not happen on LuaLaTeX Computer Modern defaults, or
 > >  > in PDFLaTeX).
 > >  > This can be seen in the top right section of the linked image,
 > >  > on the third and fourth fractions from the right.
 > >
 > >I don't think that LuaLaTeX does any correction here.  I suppose that
 > >the position of the superscript is a little bit too heigh in TG
 > >Pagella so that TeX has to lower the complete denominator accordingly.
 > >
 > >The same happens if you insert the line
 > >
 > >   \frac{\Big|\delta}{\Big|\gamma} \;
 > >
 > 
 > I agree. In fact, I think this is, in fact, a problem with the
 > combination of LuaLaTeX with OTF TeX Gyre Pagella and unicode-math.
 > 
 > The various font parameters in cmr, it seems to me, are designed so
 > that when "normal" symbols are used with "normal" 'scripts there is
 > no shift in the numerators or denominators. This allows the
 > baselines and math-axes of numerators and denominators of adjacent
 > fractions to be aligned most of the time. That is, the \gamma's in
 >    $$\frac{\gamma}{\delta} \frac{\gamma_1}{\delta^2}$$
 > line up and the \delta's should also. That is, I think, the ideal
 > that Knuth was trying for.

I doubt that Lua[La]TeX and unicode-math are involved at all.  As far
as I can see the font itself is the culprit.  But I'm pretty sure that
Ulrik comes up with a definite answer soon.

Regards,
  Reinhard

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