Subregularity of subdifferential mappings relative to the critical set and KL property of exponent 1/2

TL;DR

This paper explores the relationship between subregularity of subdifferential mappings and the KL property of exponent 1/2 for various classes of functions, establishing equivalences under certain conditions.

Contribution

It establishes new equivalences between subregularity and KL property of exponent 1/2 for convex and nonconvex functions under specific assumptions.

Findings

Equivalence between subregularity and KL property for convex functions with continuous critical set.

KL property of exponent 1/2 is equivalent to subregularity for uniformly prox-regular functions.

Subregularity implies KL property under separation of stationary values for certain nonconvex functions.

Abstract

For a proper extended real-valued function, this work focuses on the relationship between the subregularity of its subdifferential mapping relative to the critical set and its KL property of exponent 1/2. When the function is lsc convex, we establish the equivalence between them under the continuous assumption on the critical set. Then, for the uniformly prox-regular function, under its continuity on the local minimum set, the KL property of exponent 1/2 on the local minimum set is shown to be equivalent to the subregularity of its subdifferential relative to this set. Moreover, for this class of nonconvex functions, under a separation assumption of stationary values, we show that the subregularity of its subdifferential relative to the critical set also implies its KL property of exponent $1/2$. These results provide a bridge for the two kinds of regularity, and their application is illustrated by examples.