Contents - Student subdomain for University of Bath
Contents - Student subdomain for University of Bath
Contents - Student subdomain for University of Bath
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CONTENTS 3<br />
4 Modular Methods 113<br />
4.1 Gcd in one variable . . . . . . . . . . . . . . . . . . . . . . . . . . 114<br />
4.1.1 Bounds on divisors . . . . . . . . . . . . . . . . . . . . . . 115<br />
4.1.2 The modular – integer relationship . . . . . . . . . . . . . 116<br />
4.1.3 Computing the g.c.d.: one large prime . . . . . . . . . . . 118<br />
4.1.4 Computing the g.c.d.: several small primes . . . . . . . . 120<br />
4.1.5 Computing the g.c.d.: early success . . . . . . . . . . . . . 122<br />
4.1.6 An alternative correctness check . . . . . . . . . . . . . . 122<br />
4.1.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 124<br />
4.2 Polynomials in two variables . . . . . . . . . . . . . . . . . . . . . 124<br />
4.2.1 Degree Growth in Coefficients . . . . . . . . . . . . . . . . 124<br />
4.2.2 The evaluation–interpolation relationship . . . . . . . . . 126<br />
4.2.3 G.c.d. in Z p [x, y] . . . . . . . . . . . . . . . . . . . . . . . 127<br />
4.2.4 G.c.d. in Z[x, y] . . . . . . . . . . . . . . . . . . . . . . . 128<br />
4.3 Polynomials in several variables . . . . . . . . . . . . . . . . . . . 131<br />
4.3.1 A worked example . . . . . . . . . . . . . . . . . . . . . . 132<br />
4.3.2 Converting this to an algorithm . . . . . . . . . . . . . . . 134<br />
4.3.3 Worked example continued . . . . . . . . . . . . . . . . . 135<br />
4.3.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 139<br />
4.4 Further Applications . . . . . . . . . . . . . . . . . . . . . . . . . 139<br />
4.4.1 Matrix Determinants . . . . . . . . . . . . . . . . . . . . . 139<br />
4.4.2 Resultants and Discriminants . . . . . . . . . . . . . . . . 140<br />
4.4.3 Linear Systems . . . . . . . . . . . . . . . . . . . . . . . . 140<br />
4.5 Gröbner Bases . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142<br />
4.5.1 General Considerations . . . . . . . . . . . . . . . . . . . 143<br />
4.5.2 The Hilbert Function and reduction . . . . . . . . . . . . 144<br />
4.5.3 The Modular Algorithm . . . . . . . . . . . . . . . . . . . 145<br />
4.5.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 146<br />
4.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148<br />
5 p-adic Methods 149<br />
5.1 Introduction to the factorization problem . . . . . . . . . . . . . 149<br />
5.2 Modular methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 151<br />
5.3 Factoring modulo a prime . . . . . . . . . . . . . . . . . . . . . . 151<br />
5.3.1 Berlekamp’s small p method . . . . . . . . . . . . . . . . . 151<br />
5.3.2 Berlekamp’s large p method . . . . . . . . . . . . . . . . . 151<br />
5.3.3 The Cantor–Zassenhaus method . . . . . . . . . . . . . . 151<br />
5.4 From Z p to Z? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152<br />
5.5 Hensel Lifting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155<br />
5.5.1 Linear Hensel Lifting . . . . . . . . . . . . . . . . . . . . . 155<br />
5.5.2 Quadratic Hensel Lifting . . . . . . . . . . . . . . . . . . . 158<br />
5.5.3 Hybrid Hensel Lifting . . . . . . . . . . . . . . . . . . . . 160<br />
5.6 The recombination problem . . . . . . . . . . . . . . . . . . . . . 160<br />
5.7 Univariate Factoring Solved . . . . . . . . . . . . . . . . . . . . . 161<br />
5.8 Multivariate Factoring . . . . . . . . . . . . . . . . . . . . . . . . 163<br />
5.9 Other Applications . . . . . . . . . . . . . . . . . . . . . . . . . . 163