How to "resume" alignat

Question

Minimal example:

\documentclass{report}
\usepackage{amsmath}
\begin{document}
\begin{alignat}{2}
    A \hspace{12.5pt} & \hspace{12.5pt} && A \[10pt]
    B \[10pt]
    C \hspace{12.5pt} & \hspace{12.5pt} && C \[10pt]
    D \hspace{12.5pt} & \hspace{12.5pt} && D
\end{alignat}
\begin{alignat}{2}
    A \hspace{12.5pt} & \hspace{12.5pt} && A \
\end{alignat}
\begin{equation}
    B 
\end{equation}
\begin{alignat}{2}
    C \hspace{12.5pt} & \hspace{12.5pt} && C \[10pt]
    D \hspace{12.5pt} & \hspace{12.5pt} && D
\end{alignat}
\end{document}

I'd like the B to be centered with equal vertical space between the lines.

Edit.

My original question was not sufficiently precise. I do not want the horizontal spacing between the aligned columns to change. In practice the entries will be quite wide. Please see the new example.

\documentclass{report}
\usepackage{amsmath}
\begin{document}
\begin{alignat}{2}
    A \hspace{12.5pt} & \hspace{12.5pt} && A \[10pt]
    MMMMMMMMMMMMMM \[10pt]
    C \hspace{12.5pt} & \hspace{12.5pt} && C \[10pt]
    D \hspace{12.5pt} & \hspace{12.5pt} && D
\end{alignat}
\begin{alignat}{2}
    A \hspace{12.5pt} & \hspace{12.5pt} && A \
\end{alignat}
\begin{equation}
    MMMMMMMMMMMMMM 
\end{equation}
\begin{alignat}{2}
    C \hspace{12.5pt} & \hspace{12.5pt} && C \[10pt]
    D \hspace{12.5pt} & \hspace{12.5pt} && D
\end{alignat}
\end{document}

It should look like this:

        A    A
    MMMMMMMMMMMMMM
        C    C
        D    D

score 5 · Answer 1 · answered Jan 25 '22 at 22:56

You can place equations within \intertext to pause and resume alignment.

\documentclass{report}
\usepackage{amsmath}
\begin{document}
\begin{alignat}{2}
    A \hspace{12.5pt} & \hspace{12.5pt} && A \
\intertext{[ MMMMMMMMMMMMMM ]}
    C \hspace{12.5pt} & \hspace{12.5pt} && C \[10pt]
    D \hspace{12.5pt} & \hspace{12.5pt} && D
\end{alignat}
\end{document}

Werner · Accepted Answer · 2022-01-25T22:34:21.750

You can use a gather with some box measurements (provided by \eqmathbox through eqparbox):

\documentclass{article}
\usepackage{amsmath,eqparbox}
% https://tex.stackexchange.com/a/34412/5764
\makeatletter
\NewDocumentCommand{\eqmathbox}{o O{c} m}{%
  \IfValueTF{#1}
    {\def\eqmathbox@##1##2{\eqmakebox[#1][#2]{$##1##2$}}}
    {\def\eqmathbox@##1##2{\eqmakebox{$##1##2$}}}
  \mathpalette\eqmathbox@{#3}
}
\makeatother
\begin{document}
\begin{alignat}{2}
         A \hspace{12.5pt} & \hspace{12.5pt} && AA      \[10pt]
                                  BBB                   \[10pt]
      CCCC \hspace{12.5pt} & \hspace{12.5pt} && CCCCC   \[10pt]
    DDDDDD \hspace{12.5pt} & \hspace{12.5pt} && DDDDDDD
\end{alignat}
\begin{alignat}{2}
         A \hspace{12.5pt} & \hspace{12.5pt} && AA      \
\end{alignat}
\begin{equation}
                                  BBB 
\end{equation}
\begin{alignat}{2}
      CCCC \hspace{12.5pt} & \hspace{12.5pt} && CCCCC   \[10pt]
    DDDDDD \hspace{12.5pt} & \hspace{12.5pt} && DDDDDDD
\end{alignat}
\begin{gather}
        \eqmathbox[LHS][r]{A} \hspace{25pt} \eqmathbox[RHS][l]{AA}      \[10pt]
                                  BBB                                   \[10pt]
     \eqmathbox[LHS][r]{CCCC} \hspace{25pt} \eqmathbox[RHS][l]{CCCCC}   \[10pt]
  \eqmathbox[LHS][r]{DDDDDDD} \hspace{25pt} \eqmathbox[RHS][l]{DDDDDDD}
\end{gather}
\end{document}

The Left Hand Sides are measured and stored in a box of maximum width (all right-aligned) and the Right Hand Sides are put in a different box of maximum width (all left-aligned).

You can also use an array:

\[
  \renewcommand{\arraystretch}{2}% https://tex.stackexchange.com/q/31672/5764
  \begin{array}{ r @{\hspace{25pt}} l }
         A & AA               \\
      \multicolumn{2}{c}{BBB} \\
      CCCC & CCCCC            \\
    DDDDDD & DDDDDDD
  \end{array}
\]

When I try to typeset your example I get the error Undefined control sequence. \NewDocumentCommand{\eqmathbox}{o O{c} m}{% ? — simple jack, Jan 25 '22 at 20:03
@simplejack: Add \usepackage{xparse} to your preamble. Up-to-date LaTeX distributions won't need this. — Werner, Jan 25 '22 at 20:30
Thanks, now I am able to typeset the example. However, the eqmathboxes do not seem to work with prooftrees from the package ebproof as their contents. I had to put them inside of braces to make alignat work. — simple jack, Jan 25 '22 at 20:45
@simplejack: M'kay. Can you provide some code that show the current, complete, minimal example? You can use Pastebin if you wish. — Werner, Jan 25 '22 at 21:37
@simplejack: Riiight. That's another option. For reference, I'll add it to my current answer. — Werner, Jan 25 '22 at 22:29

How to "resume" alignat

2 Answers2