\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}