# Multiple \label's error in align environment

Here is the minimal not working example:

\documentclass[12pt,letterpaper]{article}

\usepackage{lmodern}
\usepackage[T1]{fontenc}

\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}

\begin{document}
\begin{align}
\nonumber \label{SR1} &\text{Rho-DNA} \mathrel{\mathop{\longrightarrow}^{k_1}} \text{Rho}\quad&&\text{SR1} \\
\nonumber \label{SR2} &\text{Rho} + \text{GDP} \mathrel{\mathop{\longrightarrow}^{k_2}} \text{Rho-GDP}\quad&&\text{SR2} \\
\nonumber \label{SR3} &\text{Rho-GDP} + \text{GDI} \mathrel{\mathop{\longleftrightarrow}^{k_3}_{k_4}} \text{Rho-GDI}\quad&&\text{SR3} \\
\nonumber \label{SR4} &\text{Rho-GDP} + \text{GTP} \mathrel{\mathop{\rightarrow}^{k_5}} \text{Rho-GTP} + \text{GDP}\quad&&\text{SR4} \\
\end{align}

\end{document}


The error I get is:

line 0: Package amsmath Error: Multiple \label's: label 'SR1' will be lost
line 0: Package amsmath Error: Multiple \label's: label 'SR3' will be lost


What is the issue?

• \nonumber in conjunction with \label is not really useful – user31729 Jan 24 '15 at 18:49
• the \quad&&\text{SR1}like pieces look like an attempt for custom tags to me. If that is right you could instead use \tag{SR1} (and remove \nonumber). Then both the error goes away and you can actually refer to the equations. – cgnieder Jan 24 '15 at 19:07
• @ChristianHupfer sure, it was just an experiment. – user89 Jan 24 '15 at 19:07
• You might also like to take a look at the mhchem or the chemformula package. – cgnieder Jan 24 '15 at 19:11
• @close-voters: the question is less than 1 hr old! #toosoon – Paul Gessler Jan 24 '15 at 19:37

You're probably using the wrong tool for this purpose.

Either use a tabular, if you want a unique number, or align together with \tag if you want the labels to be considered like equation numbers.

\documentclass[12pt,letterpaper]{article}

\usepackage{lmodern}
\usepackage[T1]{fontenc}

\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{chemformula}

\begin{document}
$$\renewcommand{\arraystretch}{2} \begin{tabular}{ll} \ch{"Rho-DNA" ->[k\sb1] "Rho"} & \text{SR1} \\ \ch{"Rho" + "GDP" ->[k\sb2] "Rho-GDP"} & \text{SR2} \\ \ch{"Rho-GDP" + "GDI" <->[k\sb3][k\sb4] "Rho-GDI"} & \text{SR3} \\ \ch{"Rho-GDP" + "GTP" ->[k\sb5] "Rho-GTP" + "GDP"} & \text{SR4} \end{tabular}$$

\begin{align}
&\ch{"Rho-DNA"          ->[$k\sb1$]          "Rho"}             \tag{SR1}\label{SR1} \\
&\ch{"Rho" + "GDP"      ->[$k\sb2$]          "Rho-GDP"}         \tag{SR2}\label{SR2} \\
&\ch{"Rho-GDP" + "GDI" <->[$k\sb3$][$k\sb4$] "Rho-GDI"}         \tag{SR3}\label{SR3} \\
&\ch{"Rho-GDP" + "GTP"  ->[$k\sb5$]          "Rho-GTP" + "GDP"} \tag{SR4}\label{SR4}
\end{align}

\end{document}