The Jacobians of non-maximal degree
Journal of Applied Mathematics and Computational Mechanics
THE JACOBIANS OF NON-MAXIMAL DEGREE
Sylwia Lara-Dziembek, Grzegorz Biernat, Edyta Pawlak
Institute of Mathematics, Czestochowa
University of Technology
firstname.lastname@example.org, email@example.com, firstname.lastname@example.org
Received: 30 October 2016; accepted: 15 November 2016
Abstract. In the article the leading forms of the polynomial mapping having the Jacobians of non-maximal degree are considered. In particular, the mappings having two zeros at infinity are discussed.
Keywords: Jacobian, zeros at infinity
The article presents the decomposition of leading forms of the polynomial mapping of two complex variables in the case when the Jacobian of this mapping does not meet maximal degree. In particular, the structure of these forms interest us in the case where the mapping has two zeros at infinity.
2. The Jacobian having non-generic degrees
Let fm, hn be the forms of variables X, Y of degrees m, n respectively with the condition . Suppose that the Jacobian of forms fm, hn vanish and represent the structures of these forms.
Lemma. Let . Therefore
and , , , where means the greatest common divisor of the numbers m and n.
According to the Euler formula  we have
so using the Cramer rule we obtain
Because , then
so after dividing by the greatest common divisor (m, n) of the numbers m and n we receive
This means that the logarithmic derivatives of the form fm, hn respectively, satisfy equalities
Thus the forms fm, hn have the same factors.
According to formula (9) the exponents satisfy the equalities
Since the numbers are relatively prime numbers, then
and at the same time the equality hold.
This means that
Thus exactly when . However
This means that
This completes the proof.
Remark 1. Obviously we can assume that .
Corollary 1 . Let , where . If , then only zeros at infinity of the mapping (f, h) are the factors of the form fm or hn.
Corollary 2. If the numbers m and n are relatively prime and , then and . This means that the mapping (f, h) has only one zero at infinity.
Corollary 3. Let , where . Let . If the mapping (f, h) have two zeros at infinity, then
where , k and l are relatively prime, .
Remark 2. In particular, can be consider the case (we put k = l = 1, p = k +1, q = k). The mappings of this type were considered in the paper .
The Jacobians of non-maximal degree appears for the mappings with the constant Jacobian. The Jacobians Conjecture [4-9] do not occur for non trivial classes of the mappings having the constant Jacobian and one or two zeros in infinity [3, 10]. In the second case (two zeros in infinity) the leading forms of the mapping have the form given in the Corollary 2. The study of such mappings lead to the general classes of the mappings for which the Jacobian Conjecture does not take place.
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