**YouTube recording: **https://youtu.be/UdjhEgSKQus**Time: **Thursday, Feb 2, 3pm EST (8pm GMT, 9am Fri NZDT)

**Zoom:**https://gatech.zoom.us/j/8802082683

**Speaker:**Tom Zaslavsky, Binghamton University

**Title:**Matroids of gain signed graphs

**Abstract:**For standard affinographic hyperplane arrangements (a.k.a. deformations of the Type A root system arrangement or “braid” arrangement), integral gain graphs give a simpler method to compute the characteristic polynomial, a fundamental invariant. For more general affinographic arrangements (a.k.a. deformations of the Type B root system arrangement), one has to combine gains with signs. How to do this has been a puzzle. The obvious method is to put signs on top of gains. The right method is to put gains on top of signs. Laura Anderson, Ting Su, and I found out how to do this, constructing the natural matroid and the corresponding semimatroid, which latter gives the characteristic polynomial of these more general arrangements when the gain group is the additive group of integers. I will explain some of this. It does get complicated.