Has there been any research on the topic of directional derivatives of functions that are minimums of convex functions?
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z^k:\mathbb{R}^n\rightarrow\mathbb{R}\cup{+\infty}is a given convex function for eachk=1,\dots,K.And, letz:\mathbb{R}^n\rightarrow\mathbb{R}\cup{+\infty}be defined as follows:z(x) = \min_{k=1,\dots,K} z^k(x).Intuitively, the directional derivatives of the function $z$ at point $x$ in direction $d$ should match the directional derivatives of the function $z^k$ at point $x$ in direction $d$, where the function $z$ and function $z^k$ coincide at point $x$ (or where the function $z^k$ is active at point $x$). I am seeking a formal proof of this concept in the literature. – Samira Fallah Feb 14 '23 at 15:18