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Stefano Marcugini

Publications and source records attributed to Stefano Marcugini.

At least 55 records · Page 3Linked to original sources
arXiv2015

Further results on multiple coverings of the farthest-off points

Multiple coverings of the farthest-off points ($(R,μ)$-MCF codes) and the corresponding $(ρ,μ)$-saturating sets in projective spaces $PG(N,q)$ are considered. We propose and develop some methods which allow us to obtain new small $(1,μ)$-saturating sets and short $(2,μ)$-MCF codes with $μ$-density either equal to 1 (optimal saturating sets and almost perfect MCF-codes) or close to 1 (roughly $1+1/cq$, $c\ge1$). In particular, we provide new algebraic constructions and some bounds. Also, we classify minimal and optimal $(1,μ)$-saturating sets in $PG(2,q)$, $q$ small.

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arXiv2015

Unitary graphs and classification of a family of symmetric graphs with complete quotients

A finite graph $Γ$ is called $G$-symmetric if $G$ is a group of automorphisms of $Γ$ which is transitive on the set of ordered pairs of adjacent vertices of $Γ$. We study a family of symmetric graphs, called the unitary graphs, whose vertices are flags of the Hermitian unital and whose adjacency relations are determined by certain elements of the underlying finite fields. Such graphs admit the unitary groups as groups of automorphisms, and they play a significant role in the classification of a family of symmetric graphs with complete quotients such that an associated incidence structure is a doubly point-transitive linear space. We give this classification in the paper and also investigate combinatorial properties of the unitary graphs.

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arXiv2014

Tables of parameters of symmetric configurations $v_{k}$

Tables of the currently known parameters of symmetric configurations are given. Formulas for parameters of the known infinite families of symmetric configurations are presented as well. The results of the recent paper [18] are used. This work can be viewed as an appendix to [18], in the sense that the tables given here cover a much larger set of parameters.

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arXiv2014

2-semiarcs in $\mathrm{PG}(2,q)$, $q\leq 13$

A $2$-semiarc is a pointset ${\mathcal S}_k$ with the property that the number of tangent lines to ${\mathcal S}_k$ at each of its points is two. Using some theoretical results and computer aided search, the complete classification of $2$-semiarcs in PG$(2,q)$ is given for $q\leq 7,$ the spectrum of their sizes is determined for $q\leq 9$, and some results about the existence are proven for $q=11$ and $q=13.$ For several sizes of $2$-semiarcs in $\mathrm{PG}(2,q)$, $q\leq 7$, classification results have been obtained by theoretical proofs.

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arXiv2014

A probabilistic construction of small complete caps in projective spaces

In this work complete caps in $PG(N,q)$ of size $O(q^{\frac{N-1}{2}}\log^{300} q)$ are obtained by probabilistic methods. This gives an upper bound asymptotically very close to the trivial lower bound $\sqrt{2}q^{\frac{N-1}{2}}$ and it improves the best known bound in the literature for small complete caps in projective spaces of any dimension. The result obtained in the paper also gives a new upper bound for $l(m,2,q)_4$, that is the minimal length $n$ for which there exists an $[n,n-m, 4]_q2$ covering code with given $m$ and $q$.

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arXiv2014

Tables of sizes of random complete arcs in the plane $PG(2,q)$

Tables of sizes of random complete arcs in the plane $PG(2,q)$ are given. The sizes are close to the smallest known sizes of complete arcs in $PG(2,q)$, in particular, to ones constructed by Algorithm FOP (fixed order of points). The random arcs are obtained in the region $\{3\leq q\leq 46337,~q \mbox{prime}\}$.

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arXiv2013

Semiovals in PG(2,8) and PG(2,9)

The classification of all semiovals and blocking semiovals in $\mathrm{PG}(2,8)$ and in $\mathrm{PG}(2,9)$ of size less than $17$ is determined. Also, some information on the stabilizer groups and the intersection sizes with lines is given.

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arXiv2012

Classification of minimal 1-saturating sets in $PG(2,q)$, $q\leq 23$

Minimal 1-saturating sets in the projective plane $PG(2,q)$ are considered. They correspond to covering codes which can be applied to many branches of combinatorics and information theory, as data compression, compression with distortion, broadcasting in interconnection network, write-once memory or steganography (see \cite{Coh} and \cite{BF2008}). The full classification of all the minimal 1-saturating sets in PG(2,9) and PG(2,11) and the classification of minimal 1-saturating sets of smallest size in PG(2,q), $16\leq q\leq 23$ are given. These results have been found using a computer-based exhaustive search that exploits projective equivalence properties.

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arXiv2012

On constructions and parameters of symmetric configurations v_{k}

The spectrum of possible parameters of symmetric configurations is investigated. We both survey known constructions and results, and propose some new construction methods. Many new parameters are obtained, in particular for cyclic symmetric configurations, which are equivalent to deficient cyclic difference sets. Both Golomb rulers and modular Golomb rulers are a key tool in our investigation. Several new upper bounds on the minimum integer E(k) such that for each v >= E(k) there exists a symmetric configuration v_{k} are obtained. Upper bounds of the same type are provided for cyclic symmetric configurations. From the standpoint of applications, it should be noted that our results extend the range of possible parameters of LDPC codes, generalized LDPC codes, and quasi-cyclic LDPC codes.

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arXiv2011

Upper bounds on the smallest size of a complete arc in the plane PG(2,q)

New upper bounds on the smallest size t_{2}(2,q) of a complete arc in the projective plane PG(2,q) are obtained for q <= 9109. From these new bounds it follows that for q <= 2621 and q = 2659,2663,2683,2693,2753,2801, the relation t_{2}(2,q) < 4.5\sqrt{q} holds. Also, for q <= 5399 and q = 5413,5417,5419,5441,5443,5471,5483,5501,5521, we have t_{2}(2,q) < 4.8\sqrt{q}. Finally, for q <= 9067 it holds that t_{2}(2,q) < 5\sqrt{q}. The new upper bounds are obtained by finding new small complete arcs with the help of a computer search using randomized greedy algorithms.

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arXiv2011

Transitive A_6-invariant k-arcs in PG(2,q)

For $q=p^r$ with a prime $p\ge 7$ such that $q \equiv 1$ or $19\pmod {30},$ the desarguesian projective plane $PG(2,q)$ of order $q$ has a unique conjugacy class of projectivity groups isomorphic to the alternating group $A_6$ of degree 6. For a projectivity group $Γ\cong A_6$ of $PG(2,q)$, we investigate the geometric properties of the (unique) $Γ$-orbit $\mathcal{O}$ of size 90 such that the 1-point stabilizer of $Γ$ in $\mathcal O$ is a cyclic group of order 4. Here $\mathcal O$ lies either in $PG(2,q)$ or in $PG(2,q^2)$ according as 3 is a square or a non-square element in $GF(q)$. We show that if $q\geq 349$ and $q\neq 421$, then $\mathcal O$ is a 90-arc, which turns out to be complete for $q=349, 409, 529, 601,661.$ Interestingly, $\mathcal O$ is the smallest known complete arc in $PG(2,601)$ and in $PG(2,661).$ Computations are carried out by MAGMA.

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