Definition (Renyi Divergence)

Given two pmfs $p$ and $q$ with common support $\mathscr{X}$, and parameter $\alpha>0, \ \alpha\not=1$, the Renyi divergence of parameter $\alpha$ between $p$ and $q$ is: $$D_\alpha:=\frac{1}{\alpha-1}\log_2\left(\sum_{a\in\mathscr{X}}p^\alpha(a)q^{1-\alpha}(a)\right)$$