1 \documentclass[letterpaper]{article}
   2 \usepackage[utf8]{inputenc}
   3 \usepackage[american]{babel}
   4 \usepackage{amsmath}
   5 \title{}
   6 \author{}
   7 \begin{document}
   8 	\maketitle
   9 \begin{equation}
  10 \label{eq:schroedinger}
  11 \mathrm{i}\cdot\hbar\cdot\frac{\partial}{\partial t}\psi(\mathbf{r},t) \;=\; - \frac{\hbar^2}{2m}\cdot\nabla^2\psi(\mathbf{r},t) + V(\mathbf{r},t)\cdot\psi(\mathbf{r},t)
  12 \end{equation}
  13 
  14 \eqref{eq:schroedinger} is an equation.
  15 \end{document}