[Tex/LaTex] Cross-referencing between files and equation counters

counterscross-referencing

I am using package xr to cross reference between two files.

Is there a way to make the equation numbers in one of the files follow the ones in the other? What I mean is, if the last equation in file A is say (28), then the first equation in file (B) be (29) and so on.

Another question is, can this be done with counters for lemmas, theorems, etc?

Best Answer

A solution using package zref:

Document A

The first document test-A.tex writes the latest value of counter equation in the zref reference eq-last:

% test-A.tex
\documentclass{article}

\usepackage{zref-base}
\usepackage{atveryend}
\makeatletter
\AfterLastShipout{%
  \if@filesw   
    \begingroup
      \zref@setcurrent{default}{\the\value{equation}}%
      \zref@wrapper@immediate{%
        \zref@labelbyprops{eq-last}{default}%
      }%
    \endgroup
  \fi
}
\makeatother

\begin{document}
\begin{equation}E=mc^2\end{equation}
\end{document}

Remarks:

Instead of \AtEndDocument it uses the hook \AfterLastShipout that is executed after the last page is shipped out and before the .aux file is closed.
\zref@wrapper@immediate maps \write to \immediate\write in order to write into the .aux file directly. At this point deferred writing without \immediate will not work, because the last page is already shipped out and there is no next page.
The code is put inside \if@filesw and \fi. That supports \nofiles, that forbids writing to auxiliary files.

Document B

The next "book in the series" imports the references from document test-A. The reference names are prefixed with A- to avoid name clashes (\zexternaldocument):

% test-B.tex
\documentclass{article}

\usepackage{zref-xr}
\makeatletter
\zexternaldocument[A-]{test-A}
\AtBeginDocument{%
  \setcounter{equation}{\zref@extractdefault{A-eq-last}{default}{0}}%
  \zref@refused{A-eq-last}%
}
\makeatother

\begin{document}
\begin{equation}v=\frac{s}{t}\end{equation}
\end{document}

Remarks:

\zref@extractdefault is expandable and can be directly used inside the value part of \setcounter.
\zref@refused complains, if the reference is not defined. LaTeX clears the warning status for undefined refernces in \begin{document}. Thus we need \AtBeginDocument (otherwise the final "LaTeX warning: There were undefined references." might be missing).

Related Solutions

[Tex/LaTex] Cross-referencing between different files

You can use the xr package to reference to other LaTeX document.

So in chapterII.tex you say:

\usepackage{xr}
\externaldocument{chapterI}

And then can use \ref{a} like normal. You can also add a prefix:

\externaldocument[I-]{chapterI}

then you can reference it as \ref{I-a} which is useful if you have identical label names in different chapters.

Note that the normal xr doesn't add hyperlinks. It only adds the label text. The zref package can be used for this. It provides the zref-xr subpackage which gives you the same functionality and should work fine with hyperref (after all both packages are from the same author). You only need to replace \externaldocument with \zexternaldocument as well as \ref with \zref.

Note that the xr package reads the aux file, e.g. in this case, it checks chapterI.aux for references.

[Tex/LaTex] Lyx cross-referencing between branches

Let our LyX document be called mypaper.lyx. Under “Document > Settings...” we add two branches: “fulltext” and “shorttext” both with filename suffix set to “Yes”. (As mentioned, “branches” are used in LyX to manage several different variants of one document.)

When only the branch “fulltext” is activated we call this the full version of the document; when only the branch “shorttext” is activated we call this the short version of the document.
The branch “fulltext” shall contain all the details, e.g., a float table (with the label “tab:1”). Such details are placed inside a “branch box”, which is created by “Insert > Branch > 1. fulltext”. Furthermore, the branch “shorttext” will only contain a cross-reference “Table [Ref: tab:1]” to that table in the long version.

So far we got the following LyX document with two branches:

mypaper.lyx containing branch boxes

How to generate the short version mypaper-shorttext.pdf and the full version mypaper-fulltext.pdf?

First, we activate the “fulltext” branch only and compile the full version (as PDF), to which we want to refer in the short version. The file name of the output will be mypaper-fulltext.pdf as you may see in the PDF viewer.
Then, we add two lines to the LaTeX Preamble of mypaper.lyx.
```
\usepackage{xr}
\externaldocument{mypaper-fulltext}
```
where mypaper-fulltext is the filename without extension of the just created output.
Finally, we activate the “shorttext” branch only and compile the short version.

The outputs are:

fulltext and shorttext PDF

Warnings

Before compiling the short version we have to make sure that the full version is updated (that is, the full version was compiled) otherwise the references may not work correctly!
After every new start of LyX one has to compile the full version again. Only after that the short version can be created.
Changing only a label in an activated branch does not trigger LyX such that one can recompile the document. A little change of text is necessary for triggering.

Background – how does this work in LyX?

For compiling a document, LyX exports a document to a LaTeX file in a temporary directory and runs the program “pdflatex” (or similar) to create the output. Luckily LyX uses the same temporary directory when compiling the short version and the full version. Hence, the files mypaper-shorttext.tex, mypaper-shorttext.aux, mypaper-fulltext.tex, mypaper-fulltext.aux are in the same directory. By using \externaldocument{mypaper-fulltext} LaTeX will find the necessary files like mypaper-fulltext.aux. After a new start of LyX, the temporary directory is empty again. Hence, the full version needs to be compile first to create the files mypaper-fulltext.tex, mypaper-fulltext.aux.

Extensibility: If the “shorttext” branch contains labels that are referred by the long version then we need to add \externaldocument{mypaper-shorttext} to the LaTeX Preamble, too, and keep the short version compiled (updated), too. More complex scenarios with several branches are possible.