6,878 research outputs found
The Largest Subsemilattices of the Endomorphism Monoid of an Independence Algebra
An algebra \A is said to be an independence algebra if it is a matroid
algebra and every map \al:X\to A, defined on a basis of \A, can be
extended to an endomorphism of \A. These algebras are particularly well
behaved generalizations of vector spaces, and hence they naturally appear in
several branches of mathematics such as model theory, group theory, and
semigroup theory.
It is well known that matroid algebras have a well defined notion of
dimension. Let \A be any independence algebra of finite dimension , with
at least two elements. Denote by \End(\A) the monoid of endomorphisms of
\A. We prove that a largest subsemilattice of \End(\A) has either
elements (if the clone of \A does not contain any constant operations) or
elements (if the clone of \A contains constant operations). As
corollaries, we obtain formulas for the size of the largest subsemilattices of:
some variants of the monoid of linear operators of a finite-dimensional vector
space, the monoid of full transformations on a finite set , the monoid of
partial transformations on , the monoid of endomorphisms of a free -set
with a finite set of free generators, among others.
The paper ends with a relatively large number of problems that might attract
attention of experts in linear algebra, ring theory, extremal combinatorics,
group theory, semigroup theory, universal algebraic geometry, and universal
algebra.Comment: To appear in Linear Algebra and its Application
Isotropic quantum walks on lattices and the Weyl equation
We present a thorough classification of the isotropic quantum walks on
lattices of dimension for cell dimension . For there exist
two isotropic walks, namely the Weyl quantum walks presented in Ref. [G. M.
D'Ariano and P. Perinotti, Phys. Rev. A 90, 062106 (2014)], resulting in the
derivation of the Weyl equation from informational principles. The present
analysis, via a crucial use of isotropy, is significantly shorter and avoids a
superfluous technical assumption, making the result completely general.Comment: 16 pages, 1 figur
Weak Liouville-Arnold Theorems & Their Implications
This paper studies the existence of invariant smooth Lagrangian graphs for
Tonelli Hamiltonian systems with symmetries. In particular, we consider Tonelli
Hamiltonians with n independent but not necessarily involutive constants of
motion and obtain two theorems reminiscent of the Liouville-Arnold theorem.
Moreover, we also obtain results on the structure of the configuration spaces
of such systems that are reminiscent of results on the configuration space of
completely integrable Tonelli Hamiltonians.Comment: 24 pages, 1 figure; v2 corrects typo in online abstract; v3 includes
new title (was: A Weak Liouville-Arnold Theorem), re-arrangement of
introduction, re-numbering of main theorems; v4 updates the authors' email
and physical addresses, clarifies notation in section 4. Final versio
A new near octagon and the Suzuki tower
We construct and study a new near octagon of order which has its
full automorphism group isomorphic to the group and which
contains copies of the Hall-Janko near octagon as full subgeometries.
Using this near octagon and its substructures we give geometric constructions
of the -graph and the Suzuki graph, both of which are strongly
regular graphs contained in the Suzuki tower. As a subgeometry of this octagon
we have discovered another new near octagon, whose order is .Comment: 24 pages, revised version with added remarks and reference
Noncommutativity and Discrete Physics
The purpose of this paper is to present an introduction to a point of view
for discrete foundations of physics. In taking a discrete stance, we find that
the initial expression of physical theory must occur in a context of
noncommutative algebra and noncommutative vector analysis. In this way the
formalism of quantum mechanics occurs first, but not necessarily with the usual
interpretations. The basis for this work is a non-commutative discrete calculus
and the observation that it takes one tick of the discrete clock to measure
momentum.Comment: LaTeX, 23 pages, no figure
Uncovering the spatial structure of mobility networks
The extraction of a clear and simple footprint of the structure of large,
weighted and directed networks is a general problem that has many applications.
An important example is given by origin-destination matrices which contain the
complete information on commuting flows, but are difficult to analyze and
compare. We propose here a versatile method which extracts a coarse-grained
signature of mobility networks, under the form of a matrix that
separates the flows into four categories. We apply this method to
origin-destination matrices extracted from mobile phone data recorded in
thirty-one Spanish cities. We show that these cities essentially differ by
their proportion of two types of flows: integrated (between residential and
employment hotspots) and random flows, whose importance increases with city
size. Finally the method allows to determine categories of networks, and in the
mobility case to classify cities according to their commuting structure.Comment: 10 pages, 5 figures +Supplementary informatio
Stability and Invariant Random Subgroups
Consider , endowed with the normalized Hamming metric
. A finitely-generated group is \emph{P-stable} if every almost
homomorphism (i.e.,
for every , ) is close to an actual
homomorphism .
Glebsky and Rivera observed that finite groups are P-stable, while Arzhantseva
and P\u{a}unescu showed the same for abelian groups and raised many questions,
especially about P-stability of amenable groups. We develop P-stability in
general, and in particular for amenable groups. Our main tool is the theory of
invariant random subgroups (IRS), which enables us to give a characterization
of P-stability among amenable groups, and to deduce stability and instability
of various families of amenable groups.Comment: 24 pages; v2 includes minor updates and new reference
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