Structured Matrix Based Methods for Approximate Polynomial GCD i. Introduction ii. Notation 1. Approximate polynomial GCD 2. Structured and resultant matrices 3. The Euclidean algorithm 4. Matrix factorization and approximate GCDs 5. Optimization approach 6. New factorization based methods 7. A fast GCD algorithm 8. Numerical tests 9. Generalizations and further work 10. Appendix A: Distances and norms 11. Appendix B: Special matrices 12. Bibliography 13. Index. Defining and computing a greatest common divisor of two polynomials with inexact coefficients is a classical problem in symbolic numeric computation. The first part of this book reviews the main results that have been proposed so far in the literature. As usual with polynomial computations the polynomial GCD problem can be expressed in matrix form: the second part of the book focuses on this point of view and analyses the structure of the relevant matrices such as Toeplitz Toepliz block and displacement structures. New algorithms for the computation of approximate polynomial GCD are presented along with extensive numerical tests. The use of matrix structure allows in particular to lower the asymptotic computational cost from cubic to quadratic order with respect to polynomial degree. .