Variational Analysis for the Bilateral Minimal Time Function

We derive formulas for the Fréchet (singular) subdiferentials of the bilateral minimal time function $T:\mathbb{R}^n \times \mathbb{R}^n \to [0,+\infty]$ associated with a system governed by differential inclusions. As a consequence, we give a connection between the Fréchet normals to the sub-level sets of $T$ and to its epigraph. Finally, we show that the Fréchet normal cones to the sub-level set of $T$ at a point $(\alpha,\beta)$ and to epi($T$) at $((\alpha,\beta),T(\alpha,\beta))$ have the same dimension.