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lecture. - CASTLE Lab - Princeton University

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Directionally Differentiable<br />

First- and Second-Order Expansions<br />

A function g(x) is directionally differentiable at x if the directional derivatives<br />

exist for all directions h.<br />

Remark<br />

g ′ (x,h) = lim<br />

t→0 +<br />

g(x +th)−g(x)<br />

t<br />

If g(x) is directional differentiable, we can expand g(x +th) for t > 0 as<br />

g(x +th) = g(x)+tg ′ (x,h)+o(t).<br />

Boris Defourny (ORFE) Lecture 6: Perturbation Analysis in Optimization March 15,2012 17 / 26

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