Education

SIAM Review, Volume 66, Issue 2, Page 353-353, May 2024.
In this issue the Education section presents two contributions. The first paper, “The Poincaré Metric and the Bergman Theory,” by Steven G. Krantz, discusses the Poincaré metric on the unit disc in the complex space and the Bergman metric on an arbitrary domain in any dimensional complex space. To define the Bergman metric the notion of Bergman kernel is crucial. Some striking properties of the Bergman kernel are discussed briefly, and it is calculated when the domain is the open unit ball. The Bergman metric is invariant under biholomorphic maps. The paper ends by discussing several attractive applications. To incorporate invariance within models in applied science, in particular for machine learning applications, there is currently a considerable interest in non-Euclidean metrics, in invariant (under some actions) metrics, and in reproducing kernels, mostly in the real-valued framework. The Bergman theory (1921) is a special case of Aronszajn's theory of Hilbert spaces with reproducing kernels (1950). Invariant metrics are used, in particular, in the study of partial differential equations. Complex-valued kernels have some interesting connections to linear systems theory. This article sheds some new light on the Poincaré metric, the Bergman kernel, the Bergman metric, and their applications in a manner that helps the reader become accustomed to these notions and to enjoy their properties. The second paper, “Dynamics of Signaling Games,” is presented by Hannelore De Silva and Karl Sigmund and is devoted to much-studied types of interactions with incomplete information, analyzing them by means of evolutionary game dynamics. Game theory is often encountered in models describing economic, social, and biological behavior, where decisions can not only be shaped by rational arguments, but may also be influenced by other factors and players. However, it is often restricted to an analysis of equilibria. In signaling games some agents are less informed than others and try to deal with it by observing actions (signals) from better informed agents. Such signals may be even purposely wrong. This article offers a concise guided tour of outcomes of evolutionary dynamics in a number of small dimensional signaling games focusing on the replicator dynamics, the best-reply dynamics, and the adaptive dynamics (dynamics of behavioral strategies whose vector field follows the gradient of the payoff vector). Furthermore, for the model of evolution of populations of players, the authors compare these dynamics. Several interesting examples illustrate that even simple adaptation processes can lead to nonequilibrium outcomes and endless cycling. This tutorial is targeted at graduate/Ph.D. students and researchers who know the basics of game theory and want to learn examples of signaling games, together with evolutionary game theory.