Overlapping columns in tikzcd

Question

The bottom-left and bottom-right expressions don't need to be so far apart. Can I make them sit closer together? I guess that means making the outer columns overlap the middle column.

Code

\documentclass{article}
\usepackage{tikz-cd, amsmath}
\begin{document}
    \begin{tikzcd}
        & x_1 + \frac{a_{12}}{a_{11}}x_2 + \frac{a_{13}}{a_{11}}x_3 \arrow[equals, d] \\
        & 0 \arrow[equals, ld] \arrow[equals, rd] & \\
        x_1 + \frac{a_{22}}{a_{21}}x_2 + \frac{a_{23}}{a_{21}}x_3 & & x_1 + \frac{a_{32}}{a_{32}}x_2 + \frac{a_{33}}{a_{31}}x_3
    \end{tikzcd}
\end{document}

Answer 1

Is this better?

\documentclass{article}
\usepackage{tikz-cd, amsmath}

\begin{document}

    \begin{tikzcd}[column sep=-3em]
        & x_1 + \frac{a_{12}}{a_{11}}x_2 + \frac{a_{13}}{a_{11}}x_3 \arrow[equals, d] \\
        & 0 \arrow[equals, ld] \arrow[equals, rd] & \\
        x_1 + \frac{a_{22}}{a_{21}}x_2 + \frac{a_{23}}{a_{21}}x_3 & & x_1 + \frac{a_{32}}{a_{32}}x_2 + \frac{a_{33}}{a_{31}}x_3
    \end{tikzcd}

\end{document} 

Answer 2

As an alternative to @Bernard's solution, you could enclose the top entry in \mathclap to eliminate its width. Note: \mathclap requires the mathtools package, which you can use in place of amsmath.

This has the advantage of only eliminating the width of specific entries without adjusting the column spacing of the diagram as a whole.

You could reduce the column sep value as well if you desire. In addition, you could enclose part of an expression in \mathllap (overlap left) or \mathrlap (overlap right):

x_1 + \frac{a_{22}}{a_{21}}x_2 + \mathrlap{\frac{a_{23}}{a_{21}}x_3}

Here is the code:

\documentclass{article}
\usepackage{tikz-cd, mathtools}
\begin{document}
    \begin{tikzcd}
        & \mathclap{x_1 + \frac{a_{12}}{a_{11}}x_2 + \frac{a_{13}}{a_{11}}x_3} \arrow[equals, d] \\
        & 0 \arrow[equals, ld] \arrow[equals, rd] & \\
        x_1 + \frac{a_{22}}{a_{21}}x_2 + \frac{a_{23}}{a_{21}}x_3 & & x_1 + \frac{a_{32}}{a_{32}}x_2 + \frac{a_{33}}{a_{31}}x_3
    \end{tikzcd}
\end{document}