Volume 26, 2020
|Number of page(s)||45|
|Published online||16 November 2020|
Null space gradient flows for constrained optimization with applications to shape optimization*,**,***
Centre de Mathématiques Appliquées, École Polytechnique,
2 Safran Tech, Magny-les-Hameaux, France.
3 Univ. Grenoble Alpes, CNRS, Grenoble INP, LJK, 38000 Grenoble, France.
**** Corresponding author: firstname.lastname@example.org
Accepted: 1 April 2020
The purpose of this article is to introduce a gradient-flow algorithm for solving equality and inequality constrained optimization problems, which is particularly suited for shape optimization applications. We rely on a variant of the Ordinary Differential Equation (ODE) approach proposed by Yamashita (Math. Program. 18 (1980) 155–168) for equality constrained problems: the search direction is a combination of a null space step and a range space step, aiming to decrease the value of the minimized objective function and the violation of the constraints, respectively. Our first contribution is to propose an extension of this ODE approach to optimization problems featuring both equality and inequality constraints. In the literature, a common practice consists in reducing inequality constraints to equality constraints by the introduction of additional slack variables. Here, we rather solve their local combinatorial character by computing the projection of the gradient of the objective function onto the cone of feasible directions. This is achieved by solving a dual quadratic programming subproblem whose size equals the number of active or violated constraints. The solution to this problem allows to identify the inequality constraints to which the optimization trajectory should remain tangent. Our second contribution is a formulation of our gradient flow in the context of – infinite-dimensional – Hilbert spaces, and of even more general optimization sets such as sets of shapes, as it occurs in shape optimization within the framework of Hadamard’s boundary variation method. The cornerstone of this formulation is the classical operation of extension and regularization of shape derivatives. The numerical efficiency and ease of implementation of our algorithm are demonstrated on realistic shape optimization problems.
Mathematics Subject Classification: 65K10 / 49Q10 / 34C35 / 49B36 / 65L05
Key words: Nonlinear constrained optimization / gradient flows / shape and topology optimization / null space method
This work was supported by the Association Nationale de la Recherche et de la Technologie (ANRT) [grant number CIFRE 2017/0024] and by the project ANR-18-CE40-0013 SHAPO financed by the French Agence Nationale de la Recherche (ANR).
F. F. is a CIFRE PhD student, funded by SAFRAN, the support of which is kindly acknowledged. G. A. is a member of the DEFI project at INRIA Saclay Ile-de-France. The work of C.D. is partially supported by the IRS-CAOS grant from Université Grenoble-Alpes.
© The authors. Published by EDP Sciences, SMAI 2020
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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