Applications of convex analysis within mathematics

in Mathematical Programming (in press)

In this paper, we study convex analysis and its theoretical applications. We first apply important tools of convex analysis to Optimization and to Analysis. We then show various deep applications of ... [more ▼]

In this paper, we study convex analysis and its theoretical applications. We first apply important tools of convex analysis to Optimization and to Analysis. We then show various deep applications of convex analysis and especially infimal convolution in Monotone Operator Theory. Among other things, we recapture the Minty surjectivity theorem in Hilbert space, and present a new proof of the sum theorem in reflexive spaces. More technically, we also discuss autoconjugate representers for maximally monotone operators. Finally, we consider various other applications in mathematical analysis. [less ▲]

Box-Total Dual Integrality, Box-Integrality, and Equimodular Matrices

in Mathematical Programming (2020)

A polyhedron is box-integer if its intersection with any integer box {ℓ≤x≤u} is integer. We define principally box-integer polyhedra to be the polyhedra P such that kP is box-integer whenever kP is ... [more ▼]

A polyhedron is box-integer if its intersection with any integer box {ℓ≤x≤u} is integer. We define principally box-integer polyhedra to be the polyhedra P such that kP is box-integer whenever kP is integer. We characterize them in several ways, involving equimodular matrices and box-total dual integral (box-TDI) systems. A rational r×n matrix is equimodular if it has full row rank and its nonzero r×r determinants all have the same absolute value. A face-defining matrix is a full row rank matrix describing the affine hull of a face of the polyhedron. Box-TDI systems are systems which yield strong min-max relations, and the underlying polyhedron is called a box-TDI polyhedron. Our main result is that the following statements are equivalent. - The polyhedron P is principally box-integer. - The polyhedron P is box-TDI. - Every face-defining matrix of P is equimodular. - Every face of P has an equimodular face-defining matrix. - Every face of P has a totally unimodular face-defining matrix. - For every face F of P, lin(F) has a totally unimodular basis. Along our proof, we show that a cone {x:Ax≤0} is box-TDI if and only if it is box-integer, and that these properties are passed on to its polar. We illustrate the use of these characterizations by reviewing well known results about box-TDI polyhedra. We also provide several applications. The first one is a new perspective on the equivalence between two results about binary clutters. Secondly, we refute a conjecture of Ding, Zang, and Zhao about box-perfect graphs. Thirdly, we discuss connections with an abstract class of polyhedra having the Integer Carathéodory Property. Finally, we characterize the box-TDIness of the cone of conservative functions of a graph and provide a corresponding box-TDI system. [less ▲]