How to align left the matrix in bmatrix environment

Question

In the following MWE, the A and B matrices are perfectly aligned. However, the matrix C is aligning itself towards the right. How to align it towards the left?

  \begin{multline}
  A=
\begin{bmatrix}
0 & 1 & 0 & \cdots & 0\\
0 & 0 & 1 & \cdots & 0 \\
\vdots & \vdots & \vdots & \ddots & \vdots\\
0 & 0 & 0 & \cdots & 1 \\
-q_{0}&-q_{1}&-q_{2}&\cdots&-q_{n-1}
 \end{bmatrix}
  ,\,\,
  B=
  \begin{bmatrix}
   0 \\
   0  \\
   \vdots \\
    b_e
   \end{bmatrix}
   \\ 
  C =
  \begin{bmatrix}
   1 &b_1/b_0  &\cdots &b_{n-1}/b_0
   \end{bmatrix}
   \end{multline}

Answer 1

You possibly want the row matrix to be centered with respect to the top block:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{equation}
\begin{gathered}
A=\begin{bmatrix}
  0 & 1 & 0 & \cdots & 0\\
  0 & 0 & 1 & \cdots & 0 \\
  \vdots & \vdots & \vdots & \ddots & \vdots\\
  0 & 0 & 0 & \cdots & 1 \\
  -q_{0}&-q_{1}&-q_{2}&\cdots&-q_{n-1}
\end{bmatrix}
,\quad
B=\begin{bmatrix} 0 \\ 0 \\ \vdots \\ b_e \end{bmatrix}
\\[2ex]
C = \begin{bmatrix} 1 & b_1/b_0 & \cdots & b_{n-1}/b_0 \end{bmatrix}
\end{gathered}
\end{equation}

\end{document}

If you want the equals signs to be aligned, use aligned:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{equation}
\begin{aligned}
A&=\begin{bmatrix}
  0 & 1 & 0 & \cdots & 0\\
  0 & 0 & 1 & \cdots & 0 \\
  \vdots & \vdots & \vdots & \ddots & \vdots\\
  0 & 0 & 0 & \cdots & 1 \\
  -q_{0}&-q_{1}&-q_{2}&\cdots&-q_{n-1}
\end{bmatrix}
,\quad
B=\begin{bmatrix} 0 \\ 0 \\ \vdots \\ b_e \end{bmatrix}
\\[2ex]
C&=\begin{bmatrix} 1 & b_1/b_0 & \cdots & b_{n-1}/b_0 \end{bmatrix}
\end{aligned}
\end{equation}

\end{document}

Answer 2

Use align* instead of multiline. Add some alignment tabs.

As commented, multiline does not come with alignment. I would guess its intent is to right align the 2nd line, as if it were the continuation of a long equation.

\documentclass{article}
\usepackage{amsmath}
%\usepackage{unicode-math}
\begin{document}
  \begin{align*}
  A&=
\begin{bmatrix}
0 & 1 & 0 & \cdots & 0\\
0 & 0 & 1 & \cdots & 0 \\
\vdots & \vdots & \vdots & \ddots & \vdots\\
0 & 0 & 0 & \cdots & 1 \\
-q_{0}&-q_{1}&-q_{2}&\cdots&-q_{n-1}
 \end{bmatrix}
  ,\,\,
  B=
  \begin{bmatrix}
   0 \\
   0  \\
   \vdots \\
    b_e
   \end{bmatrix}
   \\[8pt]
  C &=
  \begin{bmatrix}
   1 &b_1/b_0  &\cdots &b_{n-1}/b_0
   \end{bmatrix}
   \end{align*}

\end{document}

Also, instead of \,\,, you could replace with &, which would add more gap before the B matrix.