Gaining or Losing Perspective for Piecewise-Linear Under-Estimators of Convex Univariate Functions

We study MINLO (mixed-integer nonlinear optimization) formulations of the disjunction $x\in\{0\}\cup[\ell,u]$, where $z$ is a binary indicator of $x\in[\ell,u]$ ($0 \leq \ell 1$.