We consider the problem of constructing dense lattices in ${ℝ}^n$ with a given non trivial automorphisms group. We exhibit a family of such lattices of density at least $cn{2}^{-n}$, which matches, up to a multiplicative constant, the best known density of a lattice packing. For an infinite sequence of dimensions $n$, we exhibit a finite set of lattices that come with an automorphisms group of size $n$, and a constant proportion of which achieves the aforementioned lower bound on the largest packing density. The algorithmic...

We show that the diffeomorphic type of the complement to a line arrangement in a complex projective plane P 2 depends only on the graph of line intersections if no line in the arrangement contains more than two points in which at least two lines intersect. This result also holds for some special arrangements which do not satisfy this property. However it is not true in general, see [Rybnikov G., On the fundamental group of the complement of a complex hyperplane arrangement, Funct. Anal. Appl., 2011,...

Sets which simultaneously tile Rn by applying powers of an invertible matrix and translations by a lattice are studied. Diagonal matrices A for which there exist sets that tile by powers of A and by integer translations are characterized. A sufficient condition and a necessary condition on the dilations and translations for the existence of such sets are also given. These conditions depend in an essential way on the interplay between the eigenvectors of the dilation matrix and the translation lattice...

Let $A\in {\mathbb{Z}}^2\times {\mathbb{Z}}^2$ be an expanding matrix, $𝒟\subset {\mathbb{Z}}^2$ a set with $|det(A\left)\right|$ elements and define $𝒯$ via the set equation $A𝒯=𝒯+𝒟$. If the two-dimensional Lebesgue measure of $𝒯$ is positive we call $𝒯$ a self-affine plane tile. In the present paper we are concerned with topological properties of $𝒯$. We show that the fundamental group ${\pi }_1\left(𝒯\right)$ of $𝒯$ is either trivial or uncountable and provide criteria for the triviality as well as the uncountability of ${\pi }_1\left(𝒯\right)$. Furthermore, we give a short proof of the fact that the closure of each component of $\mathrm{int}\left(𝒯\right)$ is a locally...

The paper deals with the approximation by polynomials with integer coefficients in $L_p(0,1)$, 1 ≤ p ≤ ∞. Let $P_{n,r}$ be the space of polynomials of degree ≤ n which are divisible by the polynomial $x^r{(1-x)}^r$, r ≥ 0, and let $P_{n,r}^{\mathbb{Z}}\subset P_{n,r}$ be the set of polynomials with integer coefficients. Let $\mu (P_{n,r}^{\mathbb{Z}};L_p)$ be the maximal distance of elements of $P_{n,r}$ from $P_{n,r}^{\mathbb{Z}}$ in $L_p(0,1)$. We give rather precise quantitative estimates of $\mu (P_{n,r}^{\mathbb{Z}};L₂)$ for n ≳ 6r. Then we obtain similar, somewhat less precise, estimates of $\mu (P_{n,r}^{\mathbb{Z}};L_p)$ for p ≠ 2. It follows that $\mu (P_{n,r}^{\mathbb{Z}};L_p)\asymp n^{-2r-2/p}$ as n → ∞. The results partially...