This paper presents several algorithms that compute border bases of a zero-dimensional ideal. The first relates to the FGLM algorithm as it uses a linear basis transformation. In particular, it is able to compute border bases that do not contain a reduced Gröbner basis. The second algorithm is based on a generic algorithm by Bernard Mourrain originally designed for computing an ideal basis that need not be a border basis. Our fully detailed algorithm computes a border basis of a zero-dimensional ideal from a given set of generators. To obtain concrete instructions we appeal to a degree-compatible term ordering and hence compute a border basis that contains the reduced -Gröbner basis. We show an example in which this computation actually has advantages over Buchberger's algorithm. Moreover, we formulate and prove two optimizations of the Border Basis Algorithm which reduce the dimensions of the linear algebra subproblems.
This paper presents characterizations of border bases of zero-dimensional polynomial ideals that are analogous to the known characterizations of Gröbner bases. Based on a Border Division Algorithm, a variant of the usual Division Algorithm, we characterize border bases as border prebases with one of the following equivalent properties: special generation, generation of the border form ideal, confluence of the corresponding rewrite relation, reduction of S-polynomials to zero, and lifting of syzygies. The last characterization relies on a detailed study of the relative position of the border terms and their syzygy module. In particular, a border prebases is a border basis if and only if all fundamental syzygies of neighboring border terms lift; these liftings are easy to compute.
Die vorliegende Arbeit entstand aus einem einfachen Mechanik-Problem, das auf eine trigonometrische Gleichung führte. Wir vergleichen am Beispiel dieses Problems verschiedene numerische Verfahren miteinander. Das Hauptziel dieser Arbeit ist nicht die Lösung der Gleichung -sie kann sogar exakt ermittelt werden -, sondern eine Darstellung am konkreten Beispiel, wie man numerische Lösungen gewinnen kann. Insbesondere soll die Bedeutung von Bildern für die numerischen Verfahren betont werden. Schließlich werden einige praktische Aspekte diskutiert, die nur selten konkret in der Literatur beschrieben werden. Beispielsweise bewirkt die schlechte Konditionierung des Problems, dass das Bisektionsverfahren keine eindeutige Lösung im Rahmen der Rechengenauigkeit besitzt.
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