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Thu, 22 Jan 2004 10:18:48 +0100Thu, 22 Jan 2004 10:18:48 +0100Rank two Cohen-Macaulay modules over singularities of type .....
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1467
We describe, by matrix factoizations, all the rank two maximal Cohen-Macauly modules over singularities of type ......Corina Baciu; Vivian Ene; Gerhard Pfister; Dorin Popescupreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1467Thu, 22 Jan 2004 10:18:48 +0100Maximal Cohen-Macaulay Modules over the Cone of an Elliptic Curve
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1261
Radu Laza; Gerhard Pfister; Popescu Dorinpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1261Fri, 07 Sep 2001 00:00:00 +0200On an implementation of standard bases and syzygies in SINGULAR
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/461
Hubert Grassmann; Gert-Martin Greuel; Bernd Martin; W. Neumann; Gerhard Pfister; W. Pohl; Hans Schönemann; Thomas Siebertpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/461Mon, 03 Apr 2000 00:00:00 +0200SINGULAR version 1.2 User Manual
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/473
Gert-Martin Greuel; Gerhard Pfister; Hans Schönemannpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/473Mon, 03 Apr 2000 00:00:00 +0200Advances and improvements in the theory of standard bases and syzygies
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/475
Gert-Martin Greuel; Gerhard Pfisterpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/475Mon, 03 Apr 2000 00:00:00 +0200Primary decomposition: algorithms and comparisons
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/756
W. Decker; Greuel-Martin Greuel; Gerhard Pfisterpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/756Mon, 03 Apr 2000 00:00:00 +0200The normalisation: a new algorithm, implementation and comparisons
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/775
Primary decomposition of an ideal in a polynomial ring over a field belongs to the indispensable theoretical tools in commutative algebra and algebraic geometry. Geometrically it corresponds to the decomposition of an affine variety into irreducible components and is, therefore, also an important geometric concept.The decomposition of a variety into irreducible components is, however, slightly weaker than the full primary decomposition, since the irreducible components correspond only to the minimal primes of the ideal of the variety, which is a radical ideal. The embedded components, although invisible in the decomposition of the variety itself, are, however, responsible for many geometric properties, in particular, if we deform the variety slightly. Therefore, they cannot be neglected and the knowledge of the full primary decomposition is important also in a geometric context.In contrast to the theoretical importance, one can find in mathematical papers only very few concrete examples of non-trivial primary decompositions because carrying out such a decomposition by hand is almost impossible. This experience corresponds to the fact that providing efficient algorithms for primary decomposition of an ideal I ae K[x1; : : : ; xn], K a field, is also a difficult task and still one of the big challenges for computational algebra and computational algebraic geometry.All known algorithms require Gr"obner bases respectively characteristic sets and multivariate polynomial factorization over some (algebraic or transcendental) extension of the given field K. The first practical algorithm for computing the minimal associated primes is based on characteristic sets and the Ritt-Wu process ([R1], [R2], [Wu], [W]), the first practical and general primary decomposition algorithm was given by Gianni, Trager and Zacharias [GTZ]. New ideas from homological algebra were introduced by Eisenbud, Huneke and Vasconcelos in [EHV]. Recently, Shimoyama and Yokoyama [SY] provided a new algorithm, using Gr"obner bases, to obtain the primary decompositon from the given minimal associated primes.In the present paper we present all four approaches together with some improvements and with detailed comparisons, based upon an analysis of 34 examples using the computer algebra system SINGULAR [GPS]. Since primary decomposition is a fairly complicated task, it is, therefore, best explained by dividing it into several subtasks, in particular, while sometimes only one of these subtasks is needed in practice. The paper is organized in such a way that we consider the subtasks separately and present the different approaches of the above-mentioned authors, with several tricks and improvements incorporated. Some of these improvements and the combination of certain steps from the different algorithms are essential for improving the practical performance.Wolfram Decker; Gert-Martin Greuel; Gerhard Pfister; Theo de Jongpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/775Mon, 03 Apr 2000 00:00:00 +0200Gröbner bases and algebraic geometry
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/783
After the notion of Gröbner bases and an algorithm for constructing them was introduced by Buchberger [Bu1, Bu2] algebraic geometers have used Gröbner bases as the main computational tool for many years, either to prove a theorem or to disprove a conjecture or just to experiment with examples in order to obtain a feeling about the structure of an algebraic variety. Nontrivial problems coming either from logic, mathematics or applications usually lead to nontrivial Gröbner basis computations, which is the reason why several improvements have been provided by many people and have been implemented in general purpose systems like Axiom, Maple, Mathematica, Reduce, etc., and systems specialized for use in algebraic geometry and commutative algebra like CoCoA, Macaulay and Singular. The present paper starts with an introduction to some concepts of algebraic geometry which should be understood by people with (almost) no knowledge in this field. In the second chapter we introduce standard bases (generalization of Gr"obner bases to non-well-orderings), which are needed for applications to local algebraic geometry (singularity theory), and a method for computing syzygies and free resolutions. The last chapter describes a new algorithm for computing the normalization of a reduced affine ring and gives an elementary introduction to singularity theory. Then we describe algorithms, using standard bases, to compute infinitesimal deformations and obstructions, which are basic for the deformation theory of isolated singularities. It is impossible to list all papers where Gr"obner bases have been used in local and global algebraic geometry, and even more impossible to give an overview about these contributions. We have, therefore, included only references to papers mentioned in this tutorial paper. The interested reader will find many more in the other contributions of this volume and in the literature cited there.Gert-Martin Greuel; Gerhard Pfisterpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/783Mon, 03 Apr 2000 00:00:00 +0200Algorithmic ideal theory
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/784
Algebraic geometers have used Gröbner bases as the main computational tool for many years, either to prove a theorem or to disprove a conjecture or just to experiment with examples in order to obtain a feeling about the structure of an algebraic variety. Non-trivial mathematical problems usually lead to non-trivial Gröbner basis computations, which is the reason why several improvements and efficient implementations have been provided by algebraic geometers (for example, the systems CoCoA, Macaulay and SINGULAR). The present paper starts with an introduction to some concepts of algebraic geometry which should be understood by people with (almost) no knowledge in this field. In the second chapter we introduce standard bases (generalization of Gröbner bases to non-well-orderings), which are needed for applications to local algebraic geometry (singularity theory), and a method for computing syzygies and free resolutions. In the third chapter several algorithms for primary decomposition of polynomial ideals are presented, together with a discussion of improvements and preferable choices. We also describe a newly invented algorithm for computing the normalization of a reduced affine ring. The last chapter gives an elementary introduction to singularity theory and then describes algorithms, using standard bases, to compute infinitesimal deformations and obstructions, which are basic for the deformation theory of isolated singularities. It is impossible to list all papers where Gröbner basis have been used in local and global algebraic geometry, and even more impossible to give an overview about these contributions. We have, therefore, included only a few references to papers which contain interesting applications and which are not mentioned in this tutorial paper. The interested reader will find many more in the other contributions of this volume and in the literature cited there.Gert-Martin Greuel; Gerhard Pfisterpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/784Mon, 03 Apr 2000 00:00:00 +0200Moduli spaces for torsion free modules on curve singularities I
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/804
Gert-Martin Greuel; Gerhard Pfisterarticlehttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/804Mon, 03 Apr 2000 00:00:00 +0200On moduli spaces of semiquasihomogeneous singularities
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/805
Gert-Martin Greuel; Gerhard Pfisterpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/805Mon, 03 Apr 2000 00:00:00 +0200Moduli Spaces of Semiquasihomogeneous Singularities with fixed Principal Part
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/810
Gert-Martin Greuel; Claus Hertling; Gerhard Pfisterpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/810Mon, 03 Apr 2000 00:00:00 +0200Geometric quotients of unipotent group actions II
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/813
Gert-Martin Greuel; Gerhard Pfisterpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/813Mon, 03 Apr 2000 00:00:00 +0200A family of Cohen-Macaulay Modules over Singularities of Type Xt+Y^3
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/824
Gerhard Pfister; Dorin Popescupreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/824Mon, 03 Apr 2000 00:00:00 +0200