Angle of \ddots in an uneven matrix

Question

I have the following triangle matrix with zeroes on the diagonal

\documentclass[a4paper]{memoir}
\usepackage{amsmath}
\begin{document}
\[
M = \begin{pmatrix}
    0 & a_{1,2} & a_{1,3}   & \dots     & a_{1,n}   \\
      & 0       & a_{2,3}   & \dots     & a_{2,n}   \\
      &         & 0         & \ddots    & \vdots    \\
      &         &           &           & 0
  \end{pmatrix}
\]
\end{document}

The small problem I have now, is that the dots from \ddots point from a_{2,3} to the last zero. This could lead to the impression that the diagonal is not given by the zeroes. Anyone an idea?

Answer 1

How about this

\documentclass[a4paper]{memoir}
\usepackage{amsmath}
\begin{document}
\[
M = \begin{pmatrix}
    0 & a_{1,2} & a_{1,3}   & \dots     & a_{1,n}   \\
      & 0       & a_{2,3}   & \dots     & a_{2,n}   \\
      &         & 0         & \ddots    & \vdots    \\
      &         &           &     0      & a_{n-1,n}   \\
      &         &           &           & 0
  \end{pmatrix}
\]
\end{document}

BTW: please post small compilable docs instead of sniplets. The less others have to add the more likely it is to get help.

Answer 2

With nicematrix:

\documentclass[a4paper]{memoir}
\usepackage{amsmath}
\usepackage{nicematrix}
\begin{document}
\[
\renewcommand{\arraystretch}{1.3}
M = \begin{pNiceArray}{ccwc{4mm}wc{7mm}wc{7mm}}[xdots/shorten=1mm]
    0 & a_{1,2} & a_{1,3}   & \Cdots     & a_{1,n}   \\
      & 0       & a_{2,3}   & \Cdots    & a_{2,n}   \\
      &         & \Ddots    & \Ddots[shorten-end=-2mm]    & \Vdots    \\
      &         &           & 0         & a_{n-1,n}   \\
      &         &           &           & 0
  \end{pNiceArray}
\]
\end{document}

You need several compilations (because nicematrix uses PGF/Tikz nodes under the hood).