\big\Vert is the same size as \Big\Vert and is inconsistent with e.g. \big\vert

[rohitagr]

The command \big\Vert command produces output which is the same size as \Big\Vert, which results in output inconsistent with other delimiters like \vert, as shown below:

This was produced by compiling the following with LuaLaTeX (from TeX Live 2020)

\documentclass{article}
\usepackage{unicode-math}
\setmainfont{STIX Two Text}
\setmathfont{STIX Two Math}
\begin{document}
\[
\begin{array}{ccccc}
\vert & \big\vert & \Big\vert & \bigg\vert & \Bigg\vert\\
\Vert & \big\Vert & \Big\Vert & \bigg\Vert & \Bigg\Vert
\end{array}
\]
\end{document}

[rohitagr]

I'm not familiar with OpenType, but looking at the MATH table "Vert. Construction" in FontForge, it looks like U+2016 (double vertical line, corresponding to \Vert) and U+007C (vertical line, corresponding to \vert) have different parameters. If I change the value for U+2016 to match the one for U+007C, that seems to fix this issue, but I don't know if it's the correct fix.

[tiroj]

Thanks for the analysis. I'll investigate this in the new build.

[xsrvmy]

Actually there are two distinct issues:

1. \Vert is too tall when requesting a medium sized bar. This issue stops at around \bBigg@{1.7}.
2. \vert and \Vert both use stacked bars to form their characters starting at \big instead of at a much larger size. This causes inconsistent sizes between brackets and absolute value bars.

Issue 1 requires a fix in the font or a luatex patch.
Issue 2 can be fixed by changing the math table, adding larger bar characters into the font, or calling \bBigg@.

[tiroj]

For 2.20 I have adjusted the height of the math bar characters to be consistent and have added full sets of growing forms and assemblies. Assemblies should also work for the ASCII bar U+007C, but for math it is recommended to use U+2016 (and corresponding multi-bar characters from the 2000 block).

[tiroj]

Updated sources and fonts delivered to STI Pub for testing. Issue reopened pending public release.