2022/10/31 by Gibson, Peter, Saldanha, Nicolau, Tomei, Carlos
#15A63 #51M16 #51M20 #52A40 #52B11 #52C07 #52C17 #Algebraic Geometry (math.AG) #FOS: Mathematics #Metric Geometry (math.MG)
paper · doi:10.48550/arxiv.2210.17350
We present higher dimensional versions of the classical results of Euler and Fuss, both of which are special cases of the celebrated Poncelet porism. Our results concern polytopes, specifically simplices, parallelotopes and cross polytopes, inscribed in a given ellipsoid and circumscribed to another. The statements and proofs use the language of linear algebra. Without loss, one of the ellipsoids is the unit sphere and the other one is also centered at the origin. Let A be the positive symmetric matrix taking the outer ellipsoid to the inner one. If trace A = 1, there exists a bijection between the orthogonal group O(n) and the set of such labeled simplices. Similarly, if trace A2 = 1, there are families of parallelotopes and of cross polytopes, also indexed by O(n).