Топологічний семінар Інституту математики НАН України

Geometric interpretation of First Betti numbers of smooth functions orbits

by Ірина Кузнєцова

Europe/Kiev
https://us04web.zoom.us/j/73962540227?pwd=GCURIvOodGrjfsDYH5DbsPoKb6NlMl.1 (ONLINE)

https://us04web.zoom.us/j/73962540227?pwd=GCURIvOodGrjfsDYH5DbsPoKb6NlMl.1

ONLINE

Description

Let M be either a 2-disk or a cylinder, and let f be a smooth function on M that takes constant values on the boundary ∂M, has no critical points on ∂M, and satisfies the condition that near each critical point, f can be expressed locally as a homogeneous polynomial without multiple factors. We define V as either the entire boundary ∂M (for the 2-disk) or one of its boundary components (for the cylinder). Let S′(f,V) denote the group of diffeomorphisms that preserve f and are isotopic to the identity relative to V. We prove that the first Betti number of the f-orbit is equal to the number of orbits generated by the action of S′(f,V) on the internal edges of the Kronrod-Reeb graph associated with f.