\documentclass[12pt]{article}
\pagestyle{empty}
\begin{document}
\begin{displaymath}
p_{\rm trial}^{\rm arb}({\bf r}_i) = f({\bf r}\neq{\bf r}_i)
\end{displaymath}
\end{document}
\documentclass[12pt]{article}
\pagestyle{empty}
\begin{document}
\begin{displaymath}
p_{\rm trial}^{\rm arb}({\bf r}_i) = f({\bf r}\neq{\bf r}_i)
\end{displaymath}
\end{document}
::
::
::
