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Cubic Algorithm to Compute the Dynkin Type of a Positive Definite Quasi-Cartan Matrix

Pérez C., Abarca M., Rivera D.

Fundamenta Informaticae

2018

Vol. 158, nr 4

369--384

Inflations algorithm is a procedure that appears implicitly in Ovsienko’s classical proof for the classification of positive definite integral quadratic forms. The best known upper asymptotic bound for its time complexity is an exponential one. In this paper we show that this bound can be tightened to O(n6) for the naive implementation. Also, we propose a new approach to show how to decide whether an admissible quasi-Cartan matrix is positive definite and compute the Dynkin type in just O(n3) operations taking an integer matrix as input.

Algorithms for integral solutions of a class of diophantine equations

Polak A.

Control and Cybernetics

2011

Vol. 40, no 2

491-514

In 1970 a negative solution to the tenth Hilbert problem, concerning the determination of integral solutions of diophantine equations, has been published by Y. W. Matiyasevich (see Matiyasevich, 1970). Despite this result, we can present algorithms to compute integral solutions (roots) for a wide class of quadratic diophantine equations of the form q(x) = d, where q : Zn → Z is a homogeneous quadratic form. We will focus on the roots of one (i.e., d = 1) of quadratic Euler forms of selected posets from Loupias list (see Loupias, 1975). In particular, we will describe the roots of positive definite quadratic forms and the roots of quadratic forms that are principal (see Simson, 2010a). The algorithms and results we present here are successfully used in the representation theory of finite groups and algebras.