Intersecting the sides of a polygon
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- by Anton Izosimov PDF
- Proc. Amer. Math. Soc. 150 (2022), 639-649 Request permission
Abstract:
Consider the map $S$ which sends a planar polygon $P$ to a new polygon $S(P)$ whose vertices are the intersection points of second-nearest sides of $P$. This map is the inverse of the famous pentagram map. In this paper we investigate the dynamics of the map $S$. Namely, we address the question of whether a convex polygon stays convex under iterations of $S$. Computer experiments suggest that this almost never happens. We prove that indeed the set of polygons which remain convex under iterations of $S$ has measure zero, and moreover it is an algebraic subvariety of codimension two. We also discuss the equations cutting out this subvariety, as well as their geometric meaning in the case of pentagons.References
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Additional Information
- Anton Izosimov
- Affiliation: Department of Mathematics, University of Arizona, Tucson, Arizona 85716
- MR Author ID: 951165
- Email: izosimov@math.arizona.edu
- Received by editor(s): December 3, 2020
- Received by editor(s) in revised form: March 11, 2021
- Published electronically: November 4, 2021
- Additional Notes: This work was supported by NSF grant DMS-2008021.
- Communicated by: Deane Yang
- © Copyright 2021 American Mathematical Society
- Journal: Proc. Amer. Math. Soc. 150 (2022), 639-649
- MSC (2020): Primary 37J70
- DOI: https://doi.org/10.1090/proc/15698
- MathSciNet review: 4356174