Center align* columns in math mode

Question

How can I center align columns in math mode using align* or one of the similar environments? I read that the columns in align environments align in the rlrlr pattern. How do I change this to a ccccc pattern?

\begin{align*}
    \dot{x}=&A&x+&B&u\\
    ...
\end{align*}

To explore, I used the tabular environment switching from text to math mode here. The result is what I'm looking for, but it doesn't seem like the optimal method:

    \begin{tabular}[7]{ccccccc}
        $\dot{x}$ & $=$ & $A$ & $x$ & $+$ & $B$ & $u$\\
        ...
    \end{tabular}

Is there a better way to achieve this?

Answer 1

Here's a way to implement the tabular idea you mention in your posting.

(Aside: Since B appears to be column vector, I will assume that u either is or evaluates to a scalar.)

\documentclass{article}
\usepackage{amsmath,array}
\newcolumntype{C}{>{{}}c<{{}}} % col. type for binary and relational opeators
\begin{document}
[ % start of an unnumbered display-math group
\setlength\arraycolsep{0pt} % default value: 5pt
\begin{array}{cCccCcc}
\dot{x} & = & A & x & + & B & u \[\jot]
\dot{x} & = & \begingroup \setlength\arraycolsep{5pt}
              \begin{bmatrix}
              1 & 2 & 3 & 4 \
              1 & 2 & 3 & 4 \
              1 & 2 & 3 & 4 \
              1 & 2 & 3 & 4 
              \end{bmatrix} \endgroup
                & x & + & \begin{bmatrix}
                          1 \ 2 \ 3 \ 4
                          \end{bmatrix}
                            & u
\end{array}
]
\end{document}

Answer 2

Use array or bmatrix

\documentclass[12pt]{book}
\usepackage[a4paper]{geometry}
\usepackage{mathtools}
\begin{document}
\begin{equation}
\begin{array}{ccc}
x & f+g & r + t^{2}\
a = b & \text{long text} & G = \Upsilon
\end{array}
\end{equation}
\begin{equation}
\begin{bmatrix}
a & b = b = u & c \
d & e & f \
g & h & i
\end{bmatrix}
\end{equation}
\end{document}