Conceptual

Necessary and Sufficient Criterion for Convergence to a Variational Inequality Solution

A two-part test characterising exactly which sequences in a Hilbert space converge to the unique solution of an elliptic variational inequality with unilateral constraints: the distance to the constraint set must vanish, and the inequality must hold up to a slack of epsilon_n times one plus the norm gap, with the additive constant inside the slack being what makes the condition necessary as well as sufficient. Subsumes the classical Tykhonov and Levitin-Polyak notions, both of which are shown to miss convergent sequences, and motivates the strictly sharper notion of T-well-posedness.