[Tex/LaTex] Interrupting and resuming subequations

math-modenumberingsubequations

As the title states I would like to interrupt and resume a block of equations that is inside a subequations regime. My problem arises when the interrupting stuff shall contain equations on its own:

\documentclass{article}
\usepackage{amsmath}
\usepackage[colorlinks]{hyperref}

\begin{document}
\begin{subequations}\label{eq:master}%
  \begin{align}%
    a & = b \label{eq:master:ab}\\
    c & = d \label{eq:master:cd}
  \end{align}%
\end{subequations}%
%
Some stuff in between
\begin{equation}%
   A = B\label{eq:helper}
\end{equation}
%
Resume here the subequations, i.e., continue with 1c:
\begin{subequations}%
  \begin{align}%
    e & = f \label{eq:master:ef}\\
    g & = h \label{eq:master:gh}
  \end{align}%
\end{subequations}%
Master~\eqref{eq:master}, consisting of~\eqref{eq:master:ab}, \eqref{eq:master:cd}, \eqref{eq:master:ef}, \eqref{eq:master:gh},
and helper~\eqref{eq:helper}.
\end{document}

I know how to manually fiddle with the counters, but that is not The LaTeX Way. I have seen something like that for enumerations utilizing the enumitem package. How would an elegant solution look like, that let me write

\begin{subequations}[resume]%
  \begin{align}%
    e & = f \label{eq:master:ef}\\
    g & = h \label{eq:master:gh}
  \end{align}%
\end{subequations}%

Best Answer

Here is another method.

I explain: the subequations now admit an optional argument. The expected values are resume, intermezzo, or nothing. As soon as neither resume nor intermezzo is encountered, a new potential thread is initialized: continuation goes with resume, putting stuff in-between can be anything and if it is again a subequations block it has to be flagged intermezzo.

The code takes into account that hyperref patches subequations.

One caveat: subequations block playing in the rôle of intermezzi can not be globally labeled: only the actual sub-equations may be.

\documentclass{article}
\usepackage{amsmath}
\usepackage[colorlinks]{hyperref}

% original amsmath definition
% \subequations:
% \long macro:->\refstepcounter {equation}\protected@edef \theparentequation {\theequation }\setcounter {parentequation}{\value {equation}}\setcounter {equation}{0}\def \theequation {\theparentequation \alph {equation}}\ignorespaces 

% saved by hyperref in
% > \HyOrg@subequations=\long macro:

% hyperref-patched \subequations: (\endsubequations not modified)
% > \subequations=macro:
% ->\stepcounter {equation}\protected@edef \theHparentequation {\@ifundefined {th
% eHequation}\theequation \theHequation }\addtocounter {equation}{-1}\HyOrg@subeq
% uations \def \theHequation {\theHparentequation \alph {equation}}\ignorespaces 
% .


% extending the environment
%   1. with optional parameter: expected values resume or intermezzo or none.
%   2. while keeping the hyperref customization.

\makeatletter
\def\user@resume{resume}
\def\user@intermezzo{intermezzo}
%
\newcounter{previousequation}
\newcounter{lastsubequation}
\newcounter{savedparentequation}
\setcounter{savedparentequation}{1}
% 
\renewenvironment{subequations}[1][]{%
      \def\user@decides{#1}%
      \setcounter{previousequation}{\value{equation}}%
      \ifx\user@decides\user@resume 
           \setcounter{equation}{\value{savedparentequation}}%
      \else  
      \ifx\user@decides\user@intermezzo
           \refstepcounter{equation}%
      \else
           \setcounter{lastsubequation}{0}%
           \refstepcounter{equation}%
      \fi\fi
      \protected@edef\theHparentequation{%
          \@ifundefined {theHequation}\theequation \theHequation}%
      \protected@edef\theparentequation{\theequation}%
      \setcounter{parentequation}{\value{equation}}%
      \ifx\user@decides\user@resume 
           \setcounter{equation}{\value{lastsubequation}}%
         \else
           \setcounter{equation}{0}%
      \fi
      \def\theequation  {\theparentequation  \alph{equation}}%
      \def\theHequation {\theHparentequation \alph{equation}}%
      \ignorespaces
}{%
%  \arabic{equation};\arabic{savedparentequation};\arabic{lastsubequation}
  \ifx\user@decides\user@resume
       \setcounter{lastsubequation}{\value{equation}}%
       \setcounter{equation}{\value{previousequation}}%
  \else
  \ifx\user@decides\user@intermezzo
       \setcounter{equation}{\value{parentequation}}%
  \else
       \setcounter{lastsubequation}{\value{equation}}%
       \setcounter{savedparentequation}{\value{parentequation}}%
       \setcounter{equation}{\value{parentequation}}%
  \fi\fi
%  \arabic{equation};\arabic{savedparentequation};\arabic{lastsubequation}
  \ignorespacesafterend
}
\makeatother

\begin{document}\thispagestyle{empty}

\begin{subequations}\label{eq:master}
  \begin{align}
    a & = b \label{eq:master:ab}\\
    c & = d \label{eq:master:cd}
  \end{align}
\end{subequations}
%
Some intermezzo stuff in between
\begin{equation}
   A = B\label{eq:helper}
\end{equation}
%
\begin{subequations}[intermezzo]
  \begin{align}
    C &= D\label{eq:inter1}\\
    E &= F\label{eq:inter2}
  \end{align}
\end{subequations}
Resume here the subequations, i.e., continue with 1c:
\begin{subequations}[resume]
%  \label{eq:Master} % NO! impossible here
  \begin{align}
    e & = f \label{eq:master:ef}\\
    g & = h \label{eq:master:gh}\\
    g & = h \label{eq:master:gh2}
  \end{align}
\end{subequations}
Master~\eqref{eq:master}, consisting of~\eqref{eq:master:ab},
\eqref{eq:master:cd} and \eqref{eq:master:ef}, \eqref{eq:master:gh},
\eqref{eq:master:gh2} 
and helpers \eqref{eq:helper}, \eqref{eq:inter1} and \eqref{eq:inter2}. But one
can not label the intermezzo block, only its subequations.

Some more continued stuff:
\begin{subequations}[resume]
  \begin{align}
    i & = j \label{eq:master:ij}\\
    k & = l \label{eq:master:kl}\\
    i & = j \label{eq:master:ij2}
  \end{align}
\end{subequations}
and we re-initialize again (resuming will continue from here):
\begin{subequations}
  \begin{align}
    A &= B\label{eq:final1}\\
    B &= A\label{eq:final2}
  \end{align}
\end{subequations}
Two intermezzi (my head starts spinning!):
\begin{subequations}[intermezzo]
\label{eq:Intermediate}
  \begin{align}
    A &= B\label{eq:final3}\\
    B &= A\label{eq:final4}
  \end{align}
\end{subequations}
  \begin{align}
    A &= B\label{eq:final5}\\
    B &= A\label{eq:final6}
  \end{align}
And we resume again (some aspirin please!)
\begin{subequations}[resume]
  \begin{align}
    A &= B\label{eq:final7}\\
    B &= A\label{eq:final8}
  \end{align}
\end{subequations}

So we had a new block of subequations \eqref{eq:final1}, \eqref{eq:final2},
\eqref{eq:final7}, and \eqref{eq:final8}; and in-between there were
\eqref{eq:final3}, \eqref{eq:final4}, \eqref{eq:final5}, and \eqref{eq:final6}.

\end{document}

intermezzi and resumed enumaration

Related Solutions

[Tex/LaTex] Error using subequations

I did not found any error from your given code.

But you can try this one:

\documentclass{book}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{amsthm}

\begin{document}
\renewcommand{\theequation}{1\alph{equation}}
\setcounter{equation}{0}

%\begin{subequations}
\begin{equation}%<-----------------------<
h\nu'=\frac{h\nu}{1+\gamma(1-\cos\theta)}
\end{equation}
\begin{equation}
T=h\nu-h\nu'=h\nu \frac{\gamma(1-\cos\theta)}{1+\gamma(1-\cos\theta)}
\end{equation}
\begin{equation}
\cos\theta=1-\frac{2}{(1+\gamma)^2\tan^2\phi+1}
\end{equation}
\begin{equation}
\cot\phi=(1+\gamma)\tan\frac{\theta}{2}
\end{equation}
%\end{subequations}


\end{document}

[Tex/LaTex] subequations and array in braces

(Update according to egreg's commend. Thanks!)

The first example of empheq given by Bernard is invalid if omitting the overload option when loading empheq package. For the latex file provided by Bernard, it has no problems at all. However, when I used \usepackage[overload]{empheq} in IEEEtrans with a lot other packages loaded, it will freeze the pdflatex on my computer, I cannot see why, so I loaded it without overload option. Here is the version when loading empheq without overloadoption (\empheqlbrace is the big left parenthesis. \, is just used to add extra space; the default is too tight.):

\begin{subequations}
    \begin{empheq}[left={K(A)=\empheqlbrace\,}]{align}
      & (I \otimes e^A) \psi\left(A^T \oplus (-A) \right) \\
      & (e^{A^T/2} \otimes e^{A/2}) \operatorname{sinch}\left(\frac{1}{2}[A^T \oplus (-A)]\right) \\
      & \frac{1}{2}(e^{A^T} \oplus e^A) \tau\left(\frac{1}{2}[e^T \oplus (-A)]\right),
    \end{empheq}
\end{subequations}

whose output looks like: demo image

For a question on citations, it works out of box, e.g. see the following codes:

\documentclass[a4paper,10pt]{article}

\usepackage{amsmath}
\usepackage{empheq}

\begin{document}
We refer to the subequation (\ref{eq:2}) and the whole equation (\ref{eq:all}).
\begin{subequations}
  \label{eq:all}
    \begin{empheq}[left={K(A)=\empheqlbrace\,}]{align}
      & (I \otimes e^A) \psi\left(A^T \oplus (-A) \right)
        \label{eq:1} \\
      & (e^{A^T/2} \otimes e^{A/2}) \operatorname{sinch}\left(\frac{1}{2}[A^T
        \oplus (-A)]\right)
        \label{eq:2}\\
      & \frac{1}{2}(e^{A^T} \oplus e^A) \tau\left(\frac{1}{2}[e^T \oplus
        (-A)]\right),
        \label{eq:3}
    \end{empheq}
\end{subequations}
\end{document}

which gives

Best Answer

Related Solutions

[Tex/LaTex] Error using subequations

[Tex/LaTex] subequations and array in braces

Related Question