Numbering commutative diagrams

Question

Is there a nice way to number commutative diagrams (like equations) ? When using tikz-cd I put a figure environment around it, and then there is no number anywhere. I can also use

\begin{align}
\xymatrix{Some diagram}
\end{align}

but then the number is not placed nicely corresponding to the middle of the diagram.

Answer 1

I'm not sure why you think you need a figure environment to use a tikzcd environment, that is not the case. In fact, one of the first things written in the introduction of the tikz-cd manual is

Everything inside {tikzcd} is typeset in math mode, but you will probably want to use it inside an {equation} environment or \[ ... \], so that the diagram is placed on a new line and centered.

Hence, using a random example from the manual:

\documentclass{article}
\usepackage{amsmath}
\usepackage{tikz-cd}
\begin{document}
\begin{equation}
\begin{tikzcd}
A \arrow{d} \arrow{r}[near start]{\phi}[near end]{\psi}
& B \arrow[red]{d}{\xi} \\
C \arrow[red]{r}[blue]{\eta}
& D
\end{tikzcd}
\end{equation}
\end{document}

Answer 2

This is in response to the OP's request to be ale to designate a different set of numbers and label style to commutative diagrams.

It uses my numberedblock package that was intended to numbering code blocks, but used here for commutative diagrams. It has a labeling/referencing system, and the tag location and appearance can be customized.

Unfortunately, this solution is a little inconvenient, because I cannot stick the tikzcd environment in directly as the argument to a \numblock. SO I have to put it first in a temporary box and then apply the \numblock to the box.

\documentclass{article}
\usepackage{tikz-cd}
\usepackage{numberedblock,lipsum}
\setlength\blockindent{0in}
\begin{document}
\lipsum[1]

\setbox0=\hbox{\begin{tikzcd}
R \arrow{r}{\phi} \arrow[swap]{d}{\chi} & S \arrow{d}{\Psi} \\
R/I \arrow{ur}{\psi} \arrow{r}{\Phi} & T
\end{tikzcd}}
\numblock{\nblabel{cdA}\makebox[\textwidth]{\box0}}

\lipsum[4]

\setbox0=\hbox{\begin{tikzcd}
R \arrow{r}{\phi} \arrow[swap]{d}{\chi} & S \arrow{d}{\Psi} \\
blah blah R/I \arrow{ur}{\psi} \arrow{r}{\Phi} & T (blah-blah wider)
\end{tikzcd}}
\numblock{\nblabel{cdB}\makebox[\textwidth]{\box0}}

In commutative diagrams \ref{cdA} and \ref{cdB}, we see\ldots
\end{document}