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Taurida Journal of Computer Science Theory and Mathematics, 2021 Issue 3, Pages 72–78 (Mi tvim125)

On a basic invariants of the symmetry group of complex polyhedron $\frac{1}{p}{\gamma}_{n}^{m}$

O. I. Rudnitsky

V. I. Vernadsky Crimean Federal University, Simferopol

Abstract: In a $n$-dimensional unitary space ${U}^{n}$ (${n}>4$) there are three series of regular polytopes: the regular simplex $\alpha_{n}$, the generalized cross polytopes $\beta^{m}_{n}$ and the generalized $n$-cube $\gamma^{m}_{n}$. The generalized $n$-cube has ${m}^{n}$ vertices:
$$ (\theta^{{k}_{1}},\theta^{{k}_{2}},\dots, \theta^{{k}_{n}}),$$
where ${k}_{1}, {k}_{2},\dots, {k}_{n}$ take any integral values and $\theta$ is a primitive $m$th root of unity. For a certain divisor $p$ of the number $m$ the vertices of $\gamma^{m}_{n}$ with
$$ \sum_{i=1}^{n}{{k}_{i}}\equiv 0\pmod{p}$$
(there are $qm^{n-1}$ of them if $m=pq$) determine a complex polytope $\frac{1}{p}\gamma^{m}_{n}$. The symmetry group of $\frac{1}{p}\gamma^{m}_{n}$ is the imprimitive group $G(m,p,n)$ generated by reflections. It is well known that the set of polynomials invariant with respect to $G(m,p,n)$ forms an algebra generated by $n$ algebraically independent homogeneous polynomials of degrees $m, 2m,\dots, (n-1)m, qn$ (a system of basic invariants of group $G(m,p,n)$). In this paper, we study the properties of basic invariants of group $G(m,p,n)$. It is given a positive solution to the «vertex problem» for the polytope $\frac{1}{p}\gamma^{m}_{n}$ if $p$ and $n$ is mutually prime. Namely, polynomials
$$ {V}_{s}=\sum_{{k}_{i}}(\theta^{{k}_{1}}{x}_{1}+\theta^{{k}_{2}}{x}_{2}+\dots+\theta^{{k}_{n}}{x}_{n})^{ms}, \sum_{i=1}^{n}{{k}_{i}}\equiv 0\pmod{p}, s=\overline{1,n-1} $$
are algebraically independent and are basic invariants of group $G(m,p,n)$ if $p$ and $n$ is mutually prime.

Keywords: Unitary space, reflection, basic invariant, algebra of invariants, complex polyhedron.

UDC: 514.7

MSC: 51F15, 14L24



© Steklov Math. Inst. of RAS, 2024