Derivative-Free Bilevel Optimization with Inexact Lower-Level Solutions

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Main Authors: Cesaroni, Edoardo, Liuzzi, Giampaolo, Lucidi, Stefano
Format: Preprint
Published: 2026
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author Cesaroni, Edoardo
Liuzzi, Giampaolo
Lucidi, Stefano
author_facet Cesaroni, Edoardo
Liuzzi, Giampaolo
Lucidi, Stefano
contents In this work, we propose derivative-free framework for bilevel optimization. We consider both the upper and lower-level problems with bound constraints on the variables, as well as general nonlinear constraints, assuming that first-order information (in the upper-level) is not available or it is impractical to obtain. The lower-level problem is solved with an accuracy that is progressively refined throughout the optimization process. We first analyze the case in which the upper-level problem is subject only to bound constraints, establishing convergence to Clarke-Jahn stationary points when the refinement process is allowed to reach its maximum precision. When a limitation is imposed on this refinement process, we prove convergence to approximate stationary points using an extended notion of Goldstein stationarity. Finally, we extend the proposed framework to handle more complex constraints via an exact penalty function approach, proving convergence to stationary points under suitable assumptions. A comprehensive numerical study on 160 problems from the BOLIB collection shows that the adaptive accuracy strategy consistently yields better results than fixed-precision solves, with its benefits becoming more pronounced as the required lower-level accuracy becomes more stringent.
format Preprint
id arxiv_https___arxiv_org_abs_2603_20759
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Derivative-Free Bilevel Optimization with Inexact Lower-Level Solutions
Cesaroni, Edoardo
Liuzzi, Giampaolo
Lucidi, Stefano
Optimization and Control
90C26, 90C30, 90C56
In this work, we propose derivative-free framework for bilevel optimization. We consider both the upper and lower-level problems with bound constraints on the variables, as well as general nonlinear constraints, assuming that first-order information (in the upper-level) is not available or it is impractical to obtain. The lower-level problem is solved with an accuracy that is progressively refined throughout the optimization process. We first analyze the case in which the upper-level problem is subject only to bound constraints, establishing convergence to Clarke-Jahn stationary points when the refinement process is allowed to reach its maximum precision. When a limitation is imposed on this refinement process, we prove convergence to approximate stationary points using an extended notion of Goldstein stationarity. Finally, we extend the proposed framework to handle more complex constraints via an exact penalty function approach, proving convergence to stationary points under suitable assumptions. A comprehensive numerical study on 160 problems from the BOLIB collection shows that the adaptive accuracy strategy consistently yields better results than fixed-precision solves, with its benefits becoming more pronounced as the required lower-level accuracy becomes more stringent.
title Derivative-Free Bilevel Optimization with Inexact Lower-Level Solutions
topic Optimization and Control
90C26, 90C30, 90C56
url https://arxiv.org/abs/2603.20759