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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

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