*Article* **Aspects of a Phase Transition in High-Dimensional Random Geometry**

**Axel Prüser 1,\*, Imre Kondor 2,3,4 and Andreas Engel 1**


**Abstract:** A phase transition in high-dimensional random geometry is analyzed as it arises in a variety of problems. A prominent example is the feasibility of a minimax problem that represents the extremal case of a class of financial risk measures, among them the current regulatory market risk measure Expected Shortfall. Others include portfolio optimization with a ban on short-selling, the storage capacity of the perceptron, the solvability of a set of linear equations with random coefficients, and competition for resources in an ecological system. These examples shed light on various aspects of the underlying geometric phase transition, create links between problems belonging to seemingly distant fields, and offer the possibility for further ramifications.

**Keywords:** random geometry; portfolio optimization; risk measurement; disordered systems; replica theory

**PACS:** 05.20.-y; 05.40.-a; 05.70.Fh; 87.23.Ge
