200 research outputs found
An Axiomatic Setup for Algorithmic Homological Algebra and an Alternative Approach to Localization
In this paper we develop an axiomatic setup for algorithmic homological
algebra of Abelian categories. This is done by exhibiting all existential
quantifiers entering the definition of an Abelian category, which for the sake
of computability need to be turned into constructive ones. We do this
explicitly for the often-studied example Abelian category of finitely presented
modules over a so-called computable ring , i.e., a ring with an explicit
algorithm to solve one-sided (in)homogeneous linear systems over . For a
finitely generated maximal ideal in a commutative ring we
show how solving (in)homogeneous linear systems over can be
reduced to solving associated systems over . Hence, the computability of
implies that of . As a corollary we obtain the computability
of the category of finitely presented -modules as an Abelian
category, without the need of a Mora-like algorithm. The reduction also yields,
as a by-product, a complexity estimation for the ideal membership problem over
local polynomial rings. Finally, in the case of localized polynomial rings we
demonstrate the computational advantage of our homologically motivated
alternative approach in comparison to an existing implementation of Mora's
algorithm.Comment: Fixed a typo in the proof of Lemma 4.3 spotted by Sebastian Posu
Representations of fundamental groups of 3-manifolds into PGL(3,C): Exact computations in low complexity
In this paper we are interested in computing representations of the
fundamental group of a 3-manifold into PSL(3;C) (in particular in PSL(2;C);
PSL(3;R) and PU(2; 1)). The representations are obtained by gluing decorated
tetrahedra of flags. We list complete computations (giving 0-dimensional or
1-dimensional solution sets) for the first complete hyperbolic non-compact
manifolds with finite volume which are obtained gluing less than three
tetrahedra with a description of the computer methods used to find them
The Ideal Membership Problem and Abelian Groups
Given polynomials the Ideal Membership Problem, IMP for
short, asks if belongs to the ideal generated by . In the
search version of this problem the task is to find a proof of this fact. The
IMP is a well-known fundamental problem with numerous applications, for
instance, it underlies many proof systems based on polynomials such as
Nullstellensatz, Polynomial Calculus, and Sum-of-Squares. Although the IMP is
in general intractable, in many important cases it can be efficiently solved.
Mastrolilli [SODA'19] initiated a systematic study of IMPs for ideals arising
from Constraint Satisfaction Problems (CSPs), parameterized by constraint
languages, denoted IMP(). The ultimate goal of this line of research is
to classify all such IMPs accordingly to their complexity. Mastrolilli achieved
this goal for IMPs arising from CSP() where is a Boolean
constraint language, while Bulatov and Rafiey [ArXiv'21] advanced these results
to several cases of CSPs over finite domains. In this paper we consider IMPs
arising from CSPs over `affine' constraint languages, in which constraints are
subgroups (or their cosets) of direct products of Abelian groups. This kind of
CSPs include systems of linear equations and are considered one of the most
important types of tractable CSPs. Some special cases of the problem have been
considered before by Bharathi and Mastrolilli [MFCS'21] for linear equation
modulo 2, and by Bulatov and Rafiey [ArXiv'21] to systems of linear equations
over , prime. Here we prove that if is an affine constraint
language then IMP() is solvable in polynomial time assuming the input
polynomial has bounded degree
Computing isogenies between Jacobian of curves of genus 2 and 3
We present a quasi-linear algorithm to compute isogenies between Jacobians of
curves of genus 2 and 3 starting from the equation of the curve and a maximal
isotropic subgroup of the l-torsion, for l an odd prime number, generalizing
the V\'elu's formula of genus 1. This work is based from the paper "Computing
functions on Jacobians and their quotients" of Jean-Marc Couveignes and Tony
Ezome. We improve their genus 2 case algorithm, generalize it for genus 3
hyperelliptic curves and introduce a way to deal with the genus 3
non-hyperelliptic case, using algebraic theta functions.Comment: 34 page
CHAMP: A Cherednik Algebra Magma Package
We present a computer algebra package based on Magma for performing
computations in rational Cherednik algebras at arbitrary parameters and in
Verma modules for restricted rational Cherednik algebras. Part of this package
is a new general Las Vegas algorithm for computing the head and the
constituents of a module with simple head in characteristic zero which we
develop here theoretically. This algorithm is very successful when applied to
Verma modules for restricted rational Cherednik algebras and it allows us to
answer several questions posed by Gordon in some specific cases. We could
determine the decomposition matrices of the Verma modules, the graded G-module
structure of the simple modules, and the Calogero-Moser families of the generic
restricted rational Cherednik algebra for around half of the exceptional
complex reflection groups. In this way we could also confirm Martino's
conjecture for several exceptional complex reflection groups.Comment: Final version to appear in LMS J. Comput. Math. 41 pages, 3 ancillary
files. CHAMP is available at http://thielul.github.io/CHAMP/. All results are
listed explicitly in the ancillary PDF document (currently 935 pages). Please
check the website for further update
Gauge Backgrounds and Zero-Mode Counting in F-Theory
Computing the exact spectrum of charged massless matter is a crucial step
towards understanding the effective field theory describing F-theory vacua in
four dimensions. In this work we further develop a coherent framework to
determine the charged massless matter in F-theory compactified on elliptic
fourfolds, and demonstrate its application in a concrete example. The gauge
background is represented, via duality with M-theory, by algebraic cycles
modulo rational equivalence. Intersection theory within the Chow ring allows us
to extract coherent sheaves on the base of the elliptic fibration whose
cohomology groups encode the charged zero-mode spectrum. The dimensions of
these cohomology groups are computed with the help of modern techniques from
algebraic geometry, which we implement in the software gap. We exemplify this
approach in models with an Abelian and non-Abelian gauge group and observe
jumps in the exact massless spectrum as the complex structure moduli are
varied. An extended mathematical appendix gives a self-contained introduction
to the algebro-geometric concepts underlying our framework.Comment: 41 pages + extended appendice
On the complexity of computing Gr\"obner bases for weighted homogeneous systems
Solving polynomial systems arising from applications is frequently made
easier by the structure of the systems. Weighted homogeneity (or
quasi-homogeneity) is one example of such a structure: given a system of
weights , -homogeneous polynomials are polynomials
which are homogeneous w.r.t the weighted degree
. Gr\"obner bases for weighted homogeneous systems can be
computed by adapting existing algorithms for homogeneous systems to the
weighted homogeneous case. We show that in this case, the complexity estimate
for Algorithm~\F5 \left(\binom{n+\dmax-1}{\dmax}^{\omega}\right) can be
divided by a factor . For zero-dimensional
systems, the complexity of Algorithm~\FGLM (where is the
number of solutions of the system) can be divided by the same factor
. Under genericity assumptions, for
zero-dimensional weighted homogeneous systems of -degree
, these complexity estimates are polynomial in the
weighted B\'ezout bound .
Furthermore, the maximum degree reached in a run of Algorithm \F5 is bounded by
the weighted Macaulay bound , and this bound is
sharp if we can order the weights so that . For overdetermined
semi-regular systems, estimates from the homogeneous case can be adapted to the
weighted case. We provide some experimental results based on systems arising
from a cryptography problem and from polynomial inversion problems. They show
that taking advantage of the weighted homogeneous structure yields substantial
speed-ups, and allows us to solve systems which were otherwise out of reach
Numerical Algebraic Geometry: A New Perspective on String and Gauge Theories
The interplay rich between algebraic geometry and string and gauge theories
has recently been immensely aided by advances in computational algebra.
However, these symbolic (Gr\"{o}bner) methods are severely limited by
algorithmic issues such as exponential space complexity and being highly
sequential. In this paper, we introduce a novel paradigm of numerical algebraic
geometry which in a plethora of situations overcomes these short-comings. Its
so-called 'embarrassing parallelizability' allows us to solve many problems and
extract physical information which elude the symbolic methods. We describe the
method and then use it to solve various problems arising from physics which
could not be otherwise solved.Comment: 36 page
A Combinatorial Commutative Algebra Approach to Complete Decoding
Esta tesis pretende explorar el nexo de unión que existe entre la estructura algebraica de un código lineal y el proceso de descodificación completa. Sabemos que el proceso de descodificación completa para códigos lineales arbitrarios es NP-completo, incluso si se admite preprocesamiento de los datos. Nuestro objetivo es realizar un análisis algebraico del proceso de la descodificación, para ello asociamos diferentes estructuras matemáticas a ciertas familias de códigos. Desde el punto de vista computacional, nuestra descripción no proporciona un algoritmo eficiente pues nos enfrentamos a un problema de naturaleza NP. Sin embargo, proponemos algoritmos alternativos y nuevas técnicas que permiten relajar las condiciones del problema reduciendo los recursos de espacio y tiempo necesarios para manejar dicha estructura algebraica.Departamento de Algebra, Geometría y Topologí
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