Determination of the limits for multivariate rational functions |
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Authors: | ShuiJing Xiao GuangXing Zeng |
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Institution: | 14661. Department of Mathematics, Nanchang University, Nanchang, 330031, China
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Abstract: | The purpose of this paper is to solve the problem of determining the limits of multivariate rational functions. It is essential to decide whether or not {ie1-1} for two non-zero polynomials f, g ∈ ?x 1, …, x n ] with f(0, …, 0) = g(0, …, 0) = 0. For two such polynomials f and g, we establish two necessary and sufficient conditions for the rational function {ie1-2} to have its limit 0 at the origin. Based on these theoretic results, we present an algorithm for deciding whether or not {ie1-3}, where f, g ∈ ?x 1, …, x n ] are two non-zero polynomials. The design of our algorithm involves two existing algorithms: one for computing the rational univariate representations of a complete chain of polynomials, another for catching strictly critical points in a real algebraic variety. The two algorithms are based on the well-known Wu’s method. With the aid of the computer algebraic system Maple, our algorithm has been made into a general program. In the final section of this paper, several examples are given to illustrate the effectiveness of our algorithm. |
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Keywords: | rational function limit infinitesimal element strictly critical point rational univariate represen-tation(RUR) Wu's method transfer principle |
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