Let $\lambda$ be a simple eigenvalue of a matrix $A$ with right eigenvector $x$ (normalized to $\|x\|_2=1$) and left eigenvector $y$ (normalized to $\|y\|_2=1$). The condition number $s(\lambda)^{-1}$ of the eigenvalue $\lambda$ measures its sensitivity to perturbations. What is $s(\lambda)$?