The Pentagram map and infinitesimal monodromy
The pentagram map takes a planar polygon P to a polygon P' whose vertices are the intersection points of the consecutive shortest diagonals of P. The orbit of a convex polygon under this map is a sequence of polygons that converges exponentially to a point. Furthermore, as recently proved by Glick, coordinates of that limit point can be computed as an eigenvector of a certain operator associated with the polygon. In the talk, we will show that Glick’s operator can be interpreted as the infinitesimal monodromy of the polygon. Namely, there exists a certain natural infinitesimal perturbation of a polygon, which is again a polygon but in general not closed; what Glick’s operator measures is the extent to which this perturbed polygon does not close up.
The talk will be via Zoom at: https://utoronto.zoom.us/j/99576627828