Descriptive Complexity
Speaker: JamieTitle: Descriptive Complexity
Date: 13 Oct 2022 17:30-19:00 EST
Location: SEC Level 3 NW Terrace
Food: Pizza
I will give a gentle introduction to descriptive complexity theory, which measures complexity not by the resources required by a Turing machine to solve a given problem, but by the logical operators needed to formally define the problem. The theory gives a very interesting alternative perspective on what computation is, and illuminates some subtle distinctions that ordinary complexity theory is too coarse to capture. I’ll introduce a handful of well-studied logics and talk about what resources they represent from a computational perspective, and how it is possible prove lower bounds against them. I’ll explain two of the biggest results in descriptive complexity, namely, Fagin’s Theorem and the Cai-Furer-Immerman construction. Finally, I’ll discuss what is arguably the most important open problem: finding a logic that exactly captures polynomial time over unordered structures.