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.