Published online by Cambridge University Press: 20 November 2018
In this article, we study the correspondence between the geometry of del Pezzo surfaces ${{s}_{r}}$ and the geometry of the $r$-dimensional Gosset polytopes (${{(r-4)}_{21}}$. We construct Gosset polytopes ${{(r-4)}_{21}}$ in Pic ${{S}_{r}}\,\otimes \,\mathbb{Q}$ whose vertices are lines, and we identify divisor classes in Pic ${{s}_{r}}$ corresponding to $(a-1)$-simplexes $(a\le r)$, $(r-1)$-simplexes and $(r-1)$-crosspolytopes of the polytope ${{(r-4)}_{21}}$. Then we explain how these classes correspond to skew $a$-lines$(a\le r)$, exceptional systems, and rulings, respectively.
As an application, we work on the monoidal transform for lines to study the local geometry of the polytope ${{(r-4)}_{21}}$. And we show that the Gieser transformation and the Bertini transformation induce a symmetry of polytopes ${{3}_{21}}$ and ${{4}_{21}}$, respectively.