[Tex/LaTex] Equation reference undefined when using \cref and package{amsmath}

amsmathcleverefcross-referencingequations

When I attempt to reference an equation using \cref{..} while also using the package amsmath the references appear as ?? in the outputted pdf. For example

\documentclass[]{article}
\usepackage{graphicx}
\usepackage{cleveref} %for cref
\usepackage{amsmath} %for sub equation numbers and words within equations (\text)

\begin{document}


\section{Introduction}

    \begin{equation}\label{eq:solve}
    x^2 - 5 x + 6 = 0 
    \end{equation}


    Ref: \ref{eq:solve}

    CRef: \cref{eq:solve}

\end{document}

I get the output:

enter image description here

However if the \usepackage{amsmath} is commented out the \cref works correctly.

enter image description here

Is it possible to use both together successfully?

Best Answer

I tried to look for other questions with the same problem and found none. So here's an answer: load cleveref last.

From the documentation:

The cleveref package is loaded in the usual way, by putting the line
\usepackage{cleveref}
in your document’s preamble. However, care must be taken when using cleveref in conjunction with other packages that modify LaTeX’s referencing system (see Section 11). Basically, cleveref must be loaded last.

The problem is that amsmath modifies the referencing system, in order to cope with \tag, for instance. So cleveref has to hook into the redefined macros, rather than the original ones. By loading amsmath after cleveref you don't give the package the chance to know amsmath is also requested.

Related Solutions

[Tex/LaTex] How to change the position of equation number locally if I am not using the amsmath package

Others have now posted answers, but for the record this is what I had in mind. It works with all the standard classes (article, memoir, scrartcl, etc.), but not if you load amsmath, so the AMS classes, see below.

Sample output

\documentclass{article}

\makeatletter
\let\r@eqnnum\@eqnnum
\input{leqno.clo}
\let\l@eqnnum\@eqnnum
\newcommand{\leqnos}{\let\@eqnnum\l@eqnnum}
\newcommand{\reqnos}{\let\@eqnnum\r@eqnnum}
\reqnos
\makeatother

\begin{document}

\begin{equation}
  \label{eq:x}
  x = y
\end{equation}

\begingroup\leqnos
\begin{equation}
  \label{eq:a}
  a = b
\end{equation}\endgroup
and
\begin{equation}
  \label{eq:b}
  b = a.
\end{equation}

\end{document}

If you load amsmath (directly or indirectly, via e.g. mathtools or an AMS documentclass), then as Silvio Levy points the position of the labelling is controlled by different variables. In this case you can use, the following:

\documentclass{article}

\usepackage{amsmath}
\makeatletter
\newcommand{\leqnos}{\tagsleft@true\let\veqno\@@leqno}
\newcommand{\reqnos}{\tagsleft@false\let\veqno\@@eqno}
\reqnos
\makeatother

\begin{document}

\begin{equation}
  \label{eq:x}
  x = y
\end{equation}

\begingroup\leqnos
\begin{equation}
  \label{eq:a}
  a = b
\end{equation}\endgroup
and
\begin{equation}
  \label{eq:b}
  b = a.
\end{equation}

\end{document}

[Tex/LaTex] List of equations, including equation contents and caption

Since you want a cheat sheet, I'd recommend the extract package. With a slightly different MWE:

\documentclass{article}
\usepackage[
  active,
  header=false,
  copydocumentclass=true,
  generate=\jobname-Cheatsheet,
  extract-env={equation},
  extract-cmdline={synopsis},
  ]{extract} % http://ctan.org/pkg/extract
\begin{extract*}
% Items executed in both the main and extracted document
% (extract manual, section 5.1)
\usepackage{amsmath}
\end{extract*}
\begin{extract}
% Items executed only in extracted document
\def\synopsis#1{#1}
\end{extract}
\def\synopsis#1{}
\begin{document}
First Euler observed that
\synopsis{Euler's equation tying together the five fundamental constants of mathematics}%
\begin{equation}
1 + e^{i \Pi} = 0.
\end{equation}

Then, Gauss discovered the normal distribution:
\synopsis{Normal distribution}%
\begin{equation}
P(x) = \frac{1}{{\sigma \sqrt {2\pi } }}e^{{{ - \left( {x - \mu } \right)^2 } \mathord{\left/ {\vphantom {{ - \left( {x - \mu } \right)^2 } {2\sigma ^2 }}} \right. \kern-\nulldelimiterspace} {2\sigma ^2 }}}
\end{equation}

Finally, Einstein proclaimed: 
\synopsis{Equivalence of mass and energy}%
\begin{equation}
E = m C^2
\end{equation}
\end{document}

you get an original document of:

enter image description here

and an extracted document of:

\documentclass{article}
% Items executed in both the main and extracted document
% (extract manual, section 5.1)
\usepackage{amsmath}
% Items executed only in extracted document
\def\synopsis#1{#1}

\begin{document}

\synopsis{Euler's equation tying together the five fundamental constants of mathematics}%

\begin{equation}
1 + e^{i \Pi} = 0.
\end{equation}

\synopsis{Normal distribution}%

\begin{equation}
P(x) = \frac{1}{{\sigma \sqrt {2\pi } }}e^{{{ - \left( {x - \mu } \right)^2 } \mathord{\left/ {\vphantom {{ - \left( {x - \mu } \right)^2 } {2\sigma ^2 }}} \right. \kern-\nulldelimiterspace} {2\sigma ^2 }}}
\end{equation}

\synopsis{Equivalence of mass and energy}%

\begin{equation}
E = m C^2
\end{equation}

\end{document}

and:

enter image description here

This also works with your original \caption command.

Best Answer

Related Solutions

[Tex/LaTex] How to change the position of equation number locally if I am not using the amsmath package

[Tex/LaTex] List of equations, including equation contents and caption

Related Question