Wrong (too much) vertical space above \vdots in small matrix

Question

If one uses \vdots in a smallmatrix-environment the vertical spacing above the dots is too large. It is the same spacing as in a normally sized matrix-environment.

Minimal working example:

\documentclass{minimal}
%\usepackage[T1]{fontenc}
%\usepackage{lmodern}
\usepackage{amsmath,amssymb}
%\usepackage[utf8]{inputenc}
%\usepackage{icomma}
%\usepackage[final]{microtype}
%\usepackage{mathtools}
\usepackage{mathdots}

\begin{document}

Normally sized vector
\begin{equation}
\begin{pmatrix} 0 \\ \vdots \\ 0 \end{pmatrix}
\end{equation}

Small vector with too much vertical spacing above the dots.
\begin{equation}
\left(\begin{smallmatrix} 0 \\ \vdots \\ 0 \end{smallmatrix}\right)
\end{equation}

\end{document}

(In the end, I need all the packages above, but the error already occurs in the minimal setup.)

How do I reduce the spacing (for now)? Is it eventually a package implementation error? Should I report upstream?

Answer 1

the latex definition of \vdots is identical to the one defined by knuth in plain.tex, except that it is made robust. it is constructed from three periods stacked one above the other in a \vbox. the "extra" space at the top is the consequence of the full height of a "normal" character being used for the topmost period, whereas the actual height is much less.

here is a hack that smashes the \vdots and substitutes a vertical phantom of a height that yields a more pleasing result. unfortunately, i couldn't find just a single substitution that works equally well in both situations.

\begin{document}

Normally sized vector
\begin{equation}
\begin{pmatrix} 0 \\ \vphantom{\int^0}\smash[t]{\vdots} \\ 0 \end{pmatrix}
\end{equation}

Small vector with too much vertical spacing above the dots.
\begin{equation}
\left(\begin{smallmatrix} 0 \\
 \vphantom{\int\limits^x}\smash{\vdots} \\
 0 \end{smallmatrix}\right)
\end{equation}

\end{document}