[lltx] $n\choose k$-issue with OpenType math fonts

[Philipp Stephani]

@Andreas: please use only the ZIP archive format since it's the only one
everybody can read.

Am 04.03.2011 22:50, schrieb Khaled Hosny:
> On Fri, Mar 04, 2011 at 09:53:10PM +0100, Andreas Harder wrote:
>> Hi all,
>>
>> I was asked to post this also on the LuaLaTeX-list, so here it is.
>>
>> I'm tying to draw some attention to the $n\choose k$-issue with OpenType math
>> fonts. 
>>
>> I've made some test files:
>> http://dl.dropbox.com/u/151837/OpenType-Math.7z 
>>
>> The best output is generated by LuaLaTeX (at least for Asana and Cambria). 
> 
> So you are getting the best output which, IMHO, is a good thing, what is
> the problem then? :)

"Best" here unfortunately means "not very good, but not as bad as the
others."

For the following discussion, I use the notation LN, where X is the
letter A, C, or X, depending on the font, and N is a number representing
the N-th symbol from the left. I'm only looking at the document ending
in lualatex.pdf.
A1, A2, A3, A5, A6, A7, A8, A9, A11, C1, C2, C3, C5, C6, C7, C8, C9,
C10, C11, X5, X9, X10, X11 look good.
A4, C4, X4: upper and lower part are too far away from each other; as
there is no fraction bar, they should be closer to each other than the
numerator/denominator in ACX5.
A10: numerator and denominator are too far away from the fraction bar.
X1, X3, X6, X7, X8: lower part is too far to the bottom.
X2: parentheses are too high.

The issues that occur with Computer Modern are: 4, 10, i.e. those that
also appear with A and C; these are more-or-less design problems;
someone should check if they also occur in Word. X has more issues;
LuaLaTeX + A/C can be declared okay-ish, but not perfect IMO.

It would be interesting to know whether there are established
conventions regarding the vertical gaps in fractions vs. binomials.
Personally I'd prefer a smaller gap for the latter since the bar is absent.