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А.A.Karatsuba's 80th Birthday Conference in Number Theory and Applications
May 25, 2017 10:00–10:30, Moscow, Steklov Mathematical Institute
 


The generation of an alternating group by modular additions

F. M. Malyshev

Steklov Mathematical Institute of Russian Academy of Sciences, Moscow
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F. M. Malyshev
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Abstract: We consider the set $V=\mathbb{Z}_{q}^{n}$, $n\geqslant 2$, represented by the Cartesian power of the residue ring $\mathbb{Z}_{q}=\{0,1,...\,,q-1\}$, and the integer $q \geqslant 2$. We introduce special substitutions $\pi=\pi_{(i_{1},...\,,i_{r})}\in S_{V}$ of the set $V$. Each of such substitutions is determined by a subset $\{i_{1},...\,,i_{r}\}\subseteq\{1,...\,,n\}$ and by linear order introduced on this subset, where $i_{1}$ is the low-order number and $i_{r}$ is the high-order number. The power $r$ of a subset, $1 \leqslant r \leqslant n$, has an individual value for each such substitution $\pi$ and belongs to the range specified above. Also, there are $r!$ possibilities to determine the linear order. If $\pi_{(i_{1},...\,,i_{r})}(x_{1},...\,,x_{n})=(y_{1},...\,,y_{n})$ then $y_{i}=x_{i}$ for $i\notin\{i_{1},...\,,i_{r}\}$ and
$$ \sum\limits_{t=1}^{r}y_{i_{t}}q^{r-t}\,=\,1+\sum\limits_{t=1}^{r}x_{i_{t}}q^{r-t} \pmod{q^{r}\,}. $$

With the set $\mathcal{S}=\{\pi_{1},...\,,\pi_{s}\}$ of such permutations, we associate the group $G=G_\mathcal{S}=\langle\pi_{1},...\,,\pi_{s}\rangle$ generated by this set, and the oriented graph $\Gamma=\Gamma_\mathcal{S}$ on the set of vertices $\{1,...\,,n\}$. If the permutations $\pi_{j}$ are determined by the sets of numbers $\bigl(i_1^{(j)},...\,,i_{r_j}^{(j)}\bigr)$, $j=1,...\,,s$, then the graph $\Gamma$ contains the edges $i_t^{(j)}\leftarrow i_{t+1}^{(j)}$, $t=1,...\,,r_j-1$, $j=1,...\,,s$. Such edges are oriented from the low-order numbers to the high-order ones.
Theorem. Suppose that the graph $\Gamma=\Gamma_\mathcal{S}$ is strongly connected, $\mathcal{S}=\{\pi_{1},...\,,\pi_{s}\}$, $ q \geqslant 2 $, then the group $G=G_\mathcal{S}=\langle\pi_1,\,...\,,\pi_s\rangle$ contains the alternating group $A_{V}$ of the set $V$, with the only exception for $q = 2$, $n \geqslant 3$, $r_{j} \leqslant 2$ for all $j=1,...\,,s$, when $G_\mathcal{S}=AGL(n,2)$ is the affine group of the set $GF(2)^{n}$.
The group $G_ \mathcal {S}$ coincides with the symmetry group of the set $V$, if $r_{j} = n$ for some $j\in\{1,...\,,s\}$, and $q$ is even. The converse theorem is obvious. If the graph $\Gamma_\mathcal{S}$ is not strongly connected, then the group $G_\mathcal{S}$ is imprimitive.
A main combinatorial part of the theorem proof is devoted to establishing of twice transitivity of the group $G_{\mathcal{S}}$. The completion of the proof is possible due to the classification of finite simple groups and the uniqueness theorem proved by P. Mihailescu in 2003 for a solution of the equation $x^{z}-y^{t}=1 $ in integers of large 1, $3^{2}-2^{3} = 1 $, known as the Catalan hypothesis since 1884.
Application. A color monitor having a resolution $2^{10}\times2^{10}$ cells (pixels) is today's reality. Each cell has $2^{8}$ shades. A total of $2^{23}$ “cubes” are allocated to the monitor. Here $V=GF(2)^{2^3}$, $q=2$, $n=2^{23}$. The practice of working with images assumes the potential possibility of obtaining any even substitution from $\bigl(2^{2^{23}}\bigr)!/2$ possible variants, and it is desirable to use simple machine operations.

Language: English
 
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