  A multidimensional nonnegative matrix is called polystochastic if the sum of
its entries at each line is equal to $1$. The set of all polystochastic
matrices of order $n$ and dimension $d$ is a convex polytope $\Omega_n^d$. In
the present paper, we compare known bounds on the number $V(n,d)$ of vertices
of the polytope $\Omega_n^d$, propose two constructions of vertices of
$\Omega_n^d$ based on multidimensional matrix multiplication, and list all
vertices of the polytope $\Omega_3^4$.
