A minimax theorem with applications to machine learning, signal processing, and finance

Abstract

Abstract. This paper concerns a fractional function of the form x T a/ √ x T Bx, where B is positive definite. We consider the game of choosing x from a convex set, to maximize the function, and choosing (a, B) from a convex set, to minimize it. We prove the existence of a saddle point and describe an efficient method, based on convex optimization, for computing it. We describe applications in machine learning (robust Fisher linear discriminant analysis), signal processing (robust beamforming and robust matched filtering), and finance (robust portfolio selection). In these applications, x corresponds to some design variables to be chosen, and the pair (a, B) corresponds to the statistical model, which is uncertain.

Old Bands, New Tracks—Revisiting the Band Model for Robust Hypothesis Testing

“…The existence and characterization of minimax optimal solutions, however, is an intricate question. It has received continuous attention in applied mathematics, physics, and economics since the 1950s and is still an active area of research [18]- [20].…”