Process-Based Lagrange Multipliers for Nonconvex Set-Valued Optimization
Fernando García-Castaño, Miguel Ángel Melguizo-Padial
TL;DR
This work develops a general Lagrange multiplier theory for nonconvex set-valued optimization by replacing classical linear functionals with closed convex processes as multipliers. The theory proves the existence of multiplier processes under Lipschitz-type regularity and cone-nondegeneracy, and establishes a one-to-one correspondence between multiplier processes and lower semicontinuous sublinear functions in the scalar case, yielding exact penalization without additional constraint qualifications. The framework extends separation principles beyond convexity and applies naturally to set-valued vector equilibrium problems, including infinite-dimensional examples that relax interiority assumptions. Overall, the paper provides a geometric, process-based duality that informs theory and potential algorithmic approaches for nonconvex set-valued optimization.
Abstract
We develop a Lagrange multiplier theory for nonconvex set-valued optimization problems under Lipschitz-type regularity conditions. Instead of classical continuous linear functionals, we introduce closed convex processes -- set-valued mappings whose graphs are closed convex cones -- as generalized Lagrange multipliers. This geometric framework extends separation principles beyond convexity and differentiability. We establish the existence of multiplier processes under verifiable assumptions, including Lipschitz regularity at a reference point, the existence of a bounded base of the ordering cone, and a nondegeneracy condition ensuring proper isolation of optimal values. These processes preserve global optimality: nondominated (respectively, minimal) solutions of the primal problem remain nondominated (respectively, minimal) in the penalized problem. In the scalar case, we obtain a one-to-one correspondence between multiplier processes and lower semicontinuous sublinear functions, yielding exact penalty formulations without additional constraint qualifications. An infinite-dimensional example shows that interiority conditions on the ordering cone, while sufficient, are not necessary. Applications to set-valued vector equilibrium problems are also discussed.
