Force the numbering of a specific equation when mathtools showonlyrefs is true

Question

In order to avoid wasting time in adding/removing *s to number or not equations, I use \mathtools{showonlyrefs=true} in the preamble. Nevertheless, sometimes I'd like to number unreferenced equations. For instance, if just one of two subequations is referenced I want both to be numbered.
So the question is: how can I force the numbering of an unreferenced equation (or subequation) if \mathtools{showonlyrefs=true} is used in the preamble?

Answer 1

mathtools provides \noeqref for this purpose. To show the number of an equation with label eq:abc, add \noeqref{eq:abc}. The command is similar to \nocite for citations.

\documentclass{article}
\usepackage{mathtools}
\mathtoolsset{showonlyrefs}
\begin{document}
Reference to \eqref{1}.
\noeqref{3}
\begin{gather}
a=b \label{1} \\
a=c \label{2} \\
a=d \label{3} \\
\end{gather}
\end{document}