[Tex/LaTex] Vector notation in siunitx

Question

I'm trying to use the siunitx package to format a number which is a vector (using \hat{x} to represent a vector in the x direction). Using \hat{x} leads to complaints about invalid tokens.

After seeing this question, I tried including

\sisetup{input-symbols=\hatx\haty}

\protected\def\hatx{\ensuremath{\hat{x}}}
\protected\def\haty{\ensuremath{\hat{y}}}

to my preamble. Then, I get siunitx error: "misplaced-sign-token" Misplaced sign token '+'.

For completeness, here's what I am trying now:

\documentclass{article}
\usepackage{siunitx}

\sisetup{input-symbols=\hatx\haty}

\protected\def\hatx{\ensuremath{\hat{x}}}
\protected\def\haty{\ensuremath{\hat{y}}}

\begin{document}

\begin{equation}
\vec{F} = \SI{-3.24e-20\hatx + 4.56e-18\haty}{\newton}
\end{equation}

\end{document}

Any ideas how I can get this kind of thing to work properly?

Answer 1

One way to do this is to simply use:

\vec{F} = (\num{-3.24e-20}\hatx + \num{4.56e-18}\haty) \,\si{\newton}

Code:

\documentclass{article}
\usepackage{siunitx}

\protected\def\hatx{\ensuremath{\hat{x}}}
\protected\def\haty{\ensuremath{\hat{y}}}

\begin{document}
\SI{1234}{\newton}

\num{1234}\,\si{\newton}

\begin{equation}
    \vec{F} = (\num{-3.24e-20}\hatx + \num{4.56e-18}\haty) \,\si{\newton}
\end{equation}
\end{document}