\documentclass[12pt]{article} \pagestyle{empty} \begin{document} \begin{displaymath} P_{\rm select}^{\rm dihed}\left(\phi_{g_1,f,p,q}(k)\right) = { { {{p_{\rm trial}^{\rm ideal}\left(\phi_{g_1,f,p,q}(k)\right)}\over{ p_{\rm trial}^{\rm arb}\left(\phi_{g_1,f,p,q}(k)\right)}} w_{\rm bias}^{\rm fe}(k) \exp\left[-\beta \sum_{a=1}^{n_{\rm g}(n)} u_{\rm con}\left(\phi_{g_a,f,p,q}(k)\right)\right] } \over { W_{\rm dihed}(j) } } \end{displaymath} \end{document}