Augmented matrix

Question

Is it possible for me to insert a vertical dotted line between the last two columns?

\begin{pmatrix}
  1  & -1 &  0 &  0 & \cdots & 0 & a_1 \\
  0  &  1 & -1 &  0 & \cdots & 0 & a_2 \\
  0  &  0 &  1 & -1 & \cdots & 0 & a_3 \\
  \vdots  & \vdots  & \vdots & \vdots & \ddots & \vdots \\
  -1 &  0 &  0 &  0 & \cdots & 1 & a_n \\
\end{pmatrix}

Does this answer your question? What's the best way make an "augmented" coefficient matrix? — Andrew Stacey, Sep 11 '22 at 15:49
@AndrewStacey: The linked question doesn't have the dotted line requested by OP. — Sandy G, Sep 11 '22 at 18:19
@SandyG It has a dashed one that I would be willing to bet could be converted to a dotted line, and it has a nicematrix solution that could be augmented with the answer below. I would say that they are sufficiently similar that the answers here would be acceptable there and then they're all kept together for future questioners. — Andrew Stacey, Sep 11 '22 at 19:10

score 7 · Answer 1 · answered Sep 11 '22 at 15:09

Here is a solution with {pNiceArray} of nicematrix.

\documentclass{article}
\usepackage{nicematrix}
\begin{document}
[\begin{pNiceArray}{cccccc:c}
1&-1&0&0&\cdots&0&a_1\
0&1&-1&0&\cdots&0&a_2\
0&0&1&-1&\cdots&0&a_3\
\vdots&\vdots&\vdots&\vdots&\ddots&\vdots\
-1&0&0&0&\cdots&1&a_n
\end{pNiceArray}]
\end{document}

You need several compilations because of the PGF/Tikz nodes used under the hood by nicematrix.

Celdor · Answer 2 · 2022-09-11T15:33:24.777

Use last column as a 1 row matrix besides the row where you want \vdots centred

\documentclass{article}
\usepackage{array,arydshln}
\begin{document}
\[
  \left(
    \begin{array}{@{} *6{c};{1pt/2pt}c @{}}
      1  & -1 & 0  & 0  & \cdots & 0 & a_1   \\
      0  & 1  & -1 & 0  & \cdots & 0 & a_2   \\
      0  & 0  & 1  & -1 & \cdots & 0 & a_3   \\
      \vdots & \vdots & \vdots & \vdots & \ddots & \vdots \\
      -1 & 0  & 0  & 0  & \cdots & 1 & a_{n} \\
    \end{array}
  \right)
\]
\end{document}

Augmented matrix

2 Answers2