# Alignment within the equation environment

This is the state of affairs:

The goal is to horizontally center the symbols over their expressions within an equation environment. So A is centered over the first matrix, x centered over the first vector and b centered over the final vector.

MWE:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

$$\begin{split} % {\bf{A}} x & = b \\ % \left[ \begin{array}{cc} 1 & 0 \\ 0 & 1 \\ \end{array} \right] % \left[ \begin{array}{c} x_1 \\ x_2 \end{array} \right] &= % \left[ \begin{array}{c} b_1 \\ b_2 \end{array} \right] % \end{split}$$

\end{document}


These posts do not seem to offer readily a solution:

Complicated alignment within multiline equation

Aligning Multiline Matrix Equations

Aligning equations with text with alignat

Difference between align and alignat environments

TeXShop 3.58, distribution TeXLive - 2015

With array you can obtain the following:
\documentclass{article}
$$\arraycolsep=1pt \begin{array}{cccc} \mathbf{A} & \mathbf{x} & = & \mathbf{b} \\ \begin{bmatrix} 1 & 0 \\ 0 & 1 \\ \end{bmatrix} & \begin{bmatrix} x_1 \\ x_2 \end{bmatrix} & = & \begin{bmatrix} b_1 \\ b_2 \end{bmatrix} \end{array}$$