答案1
您可以命名箭头并在它们之间制作(幻影)箭头。
\documentclass{article}
\usepackage{tikz-cd}
\begin{document}
\[
\begin{tikzcd}[sep=large]
A' \arrow[r,"\alpha_1"] \arrow[d,"\psi",""{name=D1}] &
A \arrow[r,"\alpha_2"] \arrow[d,"\varphi",""{name=D2}] &
A'' \arrow[d,"\theta",""{name=D3}]\\
B' \arrow[r,"\beta_1"] &
B\arrow[r,"\beta_2"] &
B''
\arrow[phantom,from=D1,to=D2,"\scriptstyle\Sigma_1"]
\arrow[phantom,from=D2,to=D3,"\scriptstyle\Sigma_2"]
\end{tikzcd}
\]
\end{document}
答案2
一种方法是将网格的大小增加到 3x5。这样\Sigma
s 就位于第二行、第 2 列和第 4 列。
如果您希望\Sigma
s 与\psi
、\varphi
和大小相同\theta
,则可以使用\scriptstyle{\Sigma_1}
。
以下是代码:
\documentclass{article}
\usepackage{tikz-cd}
\begin{document}
\[\begin{tikzcd}[column sep=.5cm]
A'\arrow[rr,"\alpha_1"]\arrow[dd,"\psi"] && A\arrow[rr,"\alpha_2"]\arrow[dd,"\varphi"] && A''\arrow[dd,"\theta"]\\
& \Sigma_1 && \Sigma_2\\
B'\arrow[rr,"\beta_1"] && B\arrow[rr,"\beta_2"] && B''
\end{tikzcd}\]
\end{document}