[Tex/LaTex] LaTeX gives warning – empty label `’ multiply defined

cross-referencingwarnings

I have a LaTeX document that works fine, but it does give a warning message every time I compile it. Here is the text of the warning message:

LaTeX Warning: Label `' multiply defined.

The name of the label that is multiply defined appears to be an empty string. I am confused about this, but I have had trouble searching for it online because the key element is the empty string, which does not make for a good search term. Does anyone know what this warning message could mean?

I can post details of the document in question as needed, but at this point I have no idea what parts could be important.

Got it. I guess I didn't realize that bibliography items counted as labels – since I never had any intention of referring to them anywhere, I left all of their labels blank initially.

Best Answer

A label is something that you create in a document. So, you'll want to look through your document for something like \label and see how the label has been defined.

The syntax is

 \label{<label-name>}

where <label-name> is something that you create.

If you have multiple empty labels created, such as

\label{}

or something equivalent, then you'll get the error you've reported.

One way to bug-chase this and a generally good practice is to give useful and meaningful names to your labels. For example, if you have an equation, then you can write

\label{eqn:<short description of equation>}

If, for example, the label is for a section introducing the definition of a martingale, then you can write

\label{sec:defn_of_martingale}

By doing this, your labels will be meaningful and easier to understand in your source document. But also, it'll much easier to find duplicate labels.

Related Solutions

[Tex/LaTex] Warning: There were multiply-defined labels

The log message you quoted is a sort of "summary" of earlier, more detailed warnings, telling you exactly which references are undefined/multiply defined. Scroll up through the log file and you should find more detailed messages that look like the one below:

LaTeX Warning: Label `foo' multiply defined.

[Tex/LaTex] How to get rid of “multiply defined” label warning

\labels are meant to provide identifiers, that can be then referred to via commands such as \ref. After compilation (usually twice), latex replaces the \ref by a printed representation of the value of the counter captured by \label. As \ref can be used anywhere within the document, each identifier should be unique. Latex thus warns if the same identifier is defined twice.

A good scheme for generating identifiers is to use some abbreviation for the type of thing being labelled followed some memorable word or two that will remind you of what you are labelling. E.g. as Harish Kumar suggests above you might use

 \label{fig:laser-schematic}

for a label on a figure providing a schematic representation of a laser. You would then refer to this via \ref{fig:laser-schematic}.

Sample output

\documentclass{article}

\begin{document}

\begin{figure}[htp]
  \centering
  \rule{2cm}{2cm}
  \caption{Schematic view of laser}
  \label{fig:laser-schematic}
\end{figure}

Some text.

In Figure~\ref{fig:laser-schematic} we see a schematic representation
of the laser.

Some text.
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Warning: There were multiply-defined labels

[Tex/LaTex] How to get rid of “multiply defined” label warning

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