1,430 research outputs found
On Border Basis and Groebner Basis Schemes
Hilbert schemes of zero-dimensional ideals in a polynomial ring can be
covered with suitable affine open subschemes whose construction is achieved
using border bases. Moreover, border bases have proved to be an excellent tool
for describing zero-dimensional ideals when the coefficients are inexact. And
in this situation they show a clear advantage with respect to Groebner bases
which, nevertheless, can also be used in the study of Hilbert schemes, since
they provide tools for constructing suitable stratifications.
In this paper we compare Groebner basis schemes with border basis schemes. It
is shown that Groebner basis schemes and their associated universal families
can be viewed as weighted projective schemes. A first consequence of our
approach is the proof that all the ideals which define a Groebner basis scheme
and are obtained using Buchberger's Algorithm, are equal. Another result is
that if the origin (i.e. the point corresponding to the unique monomial ideal)
in the Groebner basis scheme is smooth, then the scheme itself is isomorphic to
an affine space. This fact represents a remarkable difference between border
basis and Groebner basis schemes. Since it is natural to look for situations
where a Groebner basis scheme and the corresponding border basis scheme are
equal, we address the issue, provide an answer, and exhibit some consequences.
Open problems are discussed at the end of the paper.Comment: Some typos fixed, some small corrections done. The final version of
the paper will be published on "Collectanea Mathematica
A polyhedral approach to computing border bases
Border bases can be considered to be the natural extension of Gr\"obner bases
that have several advantages. Unfortunately, to date the classical border basis
algorithm relies on (degree-compatible) term orderings and implicitly on
reduced Gr\"obner bases. We adapt the classical border basis algorithm to allow
for calculating border bases for arbitrary degree-compatible order ideals,
which is \emph{independent} from term orderings. Moreover, the algorithm also
supports calculating degree-compatible order ideals with \emph{preference} on
contained elements, even though finding a preferred order ideal is NP-hard.
Effectively we retain degree-compatibility only to successively extend our
computation degree-by-degree. The adaptation is based on our polyhedral
characterization: order ideals that support a border basis correspond
one-to-one to integral points of the order ideal polytope. This establishes a
crucial connection between the ideal and the combinatorial structure of the
associated factor spaces
Deformations of Border Bases
Here we study the problem of generalizing one of the main tools of Groebner
basis theory, namely the flat deformation to the leading term ideal, to the
border basis setting. After showing that the straightforward approach based on
the deformation to the degree form ideal works only under additional
hypotheses, we introduce border basis schemes and universal border basis
families. With their help the problem can be rephrased as the search for a
certain rational curve on a border basis scheme. We construct the system of
generators of the vanishing ideal of the border basis scheme in different ways
and study the question of how to minimalize it. For homogeneous ideals, we also
introduce a homogeneous border basis scheme and prove that it is an affine
space in certain cases. In these cases it is then easy to write down the
desired deformations explicitly.Comment: 21 page
Border bases for lattice ideals
The main ingredient to construct an O-border basis of an ideal I
K[x1,. .., xn] is the order ideal O, which is a basis of the K-vector space
K[x1,. .., xn]/I. In this paper we give a procedure to find all the possible
order ideals associated with a lattice ideal IM (where M is a lattice of Z n).
The construction can be applied to ideals of any dimension (not only
zero-dimensional) and shows that the possible order ideals are always in a
finite number. For lattice ideals of positive dimension we also show that,
although a border basis is infinite, it can be defined in finite terms.
Furthermore we give an example which proves that not all border bases of a
lattice ideal come from Gr\"obner bases. Finally, we give a complete and
explicit description of all the border bases for ideals IM in case M is a
2-dimensional lattice contained in Z 2 .Comment: 25 pages, 3 figures. Comments welcome!, MEGA'2015 (Special Issue),
Jun 2015, Trento, Ital
Toric Border Bases
We extend the theory and the algorithms of Border Bases to systems of Laurent
polynomial equations, defining "toric" roots. Instead of introducing new
variables and new relations to saturate by the variable inverses, we propose a
more efficient approach which works directly with the variables and their
inverse. We show that the commutation relations and the inversion relations
characterize toric border bases. We explicitly describe the first syzygy module
associated to a toric border basis in terms of these relations. Finally, a new
border basis algorithm for Laurent polynomials is described and a proof of its
termination is given for zero-dimensional toric ideals
The Geometry of Border Bases
The main topic of the paper is the construction of various explicit flat
families of border bases. To begin with, we cover the punctual Hilbert scheme
Hilb^\mu(A^n) by border basis schemes and work out the base changes. This
enables us to control flat families obtained by linear changes of coordinates.
Next we provide an explicit construction of the principal component of the
border basis scheme, and we use it to find flat families of maximal dimension
at each radical point. Finally, we connect radical points to each other and to
the monomial point via explicit flat families on the principal component
Solving Polynomial Equations with Equation Constraints: the Zero-dimensional Case
A zero-dimensional polynomial ideal may have a lot of complex zeros. But
sometimes, only some of them are needed. In this paper, for a zero-dimensional
ideal , we study its complex zeros that locate in another variety
where is an arbitrary ideal.
The main problem is that for a point in , its multiplicities w.r.t. and may be
different. Therefore, we cannot get the multiplicity of this point w.r.t.
by studying . A straightforward way is that first compute the points of
, then study their multiplicities w.r.t. . But the former
step is difficult to realize exactly.
In this paper, we propose a natural geometric explanation of the localization
of a polynomial ring corresponding to a semigroup order. Then, based on this
view, using the standard basis method and the border basis method, we introduce
a way to compute the complex zeros of in with their
multiplicities w.r.t. . As an application, we compute the sum of Milnor
numbers of the singular points on a polynomial hypersurface and work out all
the singular points on the hypersurface with their Milnor numbers
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