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Search Results: 1 - 10 of 4598 matches for " Csaba Schneider "
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Computing nilpotent quotients in finitely presented Lie rings
Csaba Schneider
Discrete Mathematics & Theoretical Computer Science , 1997,
Abstract: A nilpotent quotient algorithm for finitely presented Lie rings over Z (and Q) is described. The paper studies the graded and non-graded cases separately. The algorithm computes the so-called nilpotent presentation for a finitely presented, nilpotent Lie ring. A nilpotent presentation consists of generators for the abelian group and the products expressed as linear combinations for pairs formed by generators. Using that presentation the word problem is decidable in L. Provided that the Lie ring L is graded, it is possible to determine the canonical presentation for a lower central factor of L. Complexity is studied and it is shown that optimising the presentation is NP-hard. Computational details are provided with examples, timing and some structure theorems obtained from computations. Implementation in C and GAP interface are available.
A computer-based approach to the classification of nilpotent Lie algebras
Csaba Schneider
Mathematics , 2004,
Abstract: We adopt the $p$-group generation algorithm to classify small-dimensional nilpotent Lie algebras over small fields. Using an implementation of this algorithm, we list the nilpotent Lie algebras of dimension at most~9 over $\F_2$ and those of dimension at most~7 over $\F_3$ and $\F_5$.
Groups of prime-power order with a small second derived quotient
Csaba Schneider
Mathematics , 2003,
Abstract: For odd primes we prove some structure theorems for finite $p$-groups $G$, such that $G''\neq 1$ and $|G'/G''|=p^3$. Building on results of Blackburn and Hall, it is shown that $\lcs G3$ is a maximal subgroup of $G'$, the group $G$ has a central decomposition into two simpler subgroups, and, moreover, $G'$ has one of two isomorphism types.
Small derived quotients in finite p-groups
Csaba Schneider
Mathematics , 2005,
Abstract: More than 70 years ago, P. Hall showed that if $G$ is a finite $p$-group such that a term $\der G{d+1}$ of the derived series is non-trivial, then the order of the quotient $\der Gd/\der G{d+1}$ is at least $p^{2^d+1}$. Recently Mann proved that, in a finite $p$-group, Hall's lower bound can be taken for at most two distinct $d$. We improve this result and show that if $p$ is odd, then it can only be taken for two distinct $d$ in a group with order $p^6$.
The derived series of a finite p-group
Csaba Schneider
Mathematics , 2005,
Abstract: Let $G$ be a finite $p$-group, and let $\der Gd$ denote the $d$-th term of the derived series of $G$. We show, for $p\geq 5$, that $\der Gd\neq 1$ implies $\log_p\ord G\geq 2^d+3d-6$, and hence we improve a recent result by Mann.
Computing Nilpotent Quotients in Finitely Presented Lie Rings
Csaba Schneider
Mathematics , 1996,
Abstract: A nilpotent quotient algorithm for finitely presented Lie rings over Z (LieNQ) is described. The paper studies graded and non-graded cases separately. The algorithm computes the so-called nilpotent presentation for a finitely presented, nilpotent Lie ring. The nilpotent presentation consists of generators for the abelian group and the products---expressed as linear combinations---for pairs formed by generators. Using that presentation the word problem is decidable in $L$. Provided that the Lie ring $L$ is graded, it is possible to determine the canonical presentation for a lower central factor of $L$. LieNQ's complexity is studied and it is shown that optimizing the presentation is NP-hard. Computational details are provided with examples, timing and some structure theorems obtained from computations. Implementation in C and GAP 3.5 interface is available.
The isomorphism problem for universal enveloping algebras of nilpotent Lie algebras
Csaba Schneider,Hamid Usefi
Mathematics , 2010,
Abstract: In this paper we study the isomorphism problem for the universal enveloping algebras of nilpotent Lie algebras. We prove that if the characteristic of the underlying field is not~2 or~3, then the isomorphism type of a nilpotent Lie algebra of dimension at most~6 is determined by the isomorphism type of its universal enveloping algebra. Examples show that the restriction on the characteristic is necessary.
Cliques and colorings in generalized Paley graphs and an approach to synchronization
Csaba Schneider,Ana Silva
Mathematics , 2013,
Abstract: Given a finite field, one can form a directed graph using the field elements as vertices and connecting two vertices if their difference lies in a fixed subgroup of the multiplicative group. If -1 is contained in this fixed subgroup, then we obtain an undirected graph that is referred to as a generalized Paley graph. In this paper we study generalized Paley graphs whose clique and chromatic numbers coincide and link this theory to the study of the synchronization property in 1-dimensional primitive affine permutation groups.
The classification of p-nilpotent restricted Lie algebras of dimension at most 4
Csaba Schneider,Hamid Usefi
Mathematics , 2014,
Abstract: In this paper we obtain the classification of $p$-nilpotent restricted Lie algebras of dimension at most four over a perfect field of characteristic p.
The Rank of the Endomorphism Monoid of a Partition
Joao Araujo,Csaba Schneider
Mathematics , 2008,
Abstract: The rank of a semigroup is the cardinality of a smallest generating set. In this paper we compute the rank of the endomorphism monoid of a non-trivial uniform partition of a finite set, that is, the semigroup of those transformations of a finite set that leave a non-trivial uniform partition invariant. That involves proving that the rank of a wreath product of two symmetric groups is two and then use the fact that the endomorphism monoid of a partition is isomorphic to a wreath product of two full transformation semigroups. The calculation of the rank of these semigroups solves an open question.
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