Computing Real Roots of Real Polynomials
Abstract
Computing the roots of a univariate polynomial is a fundamental and longstudied problem of computational algebra with applications in mathematics, engineering, computer science, and the natural sciences. For isolating as well as for approximating all complex roots, the best algorithm known is based on an almost optimal method for approximate polynomial factorization, introduced by Pan in 2002. Pan's factorization algorithm goes back to the splitting circle method from Schoenhage in 1982. The main drawbacks of Pan's method are that it is quite involved and that all roots have to be computed at the same time. For the important special case, where only the real roots have to be computed, much simpler methods are used in practice; however, they considerably lag behind Pan's method with respect to complexity. In this paper, we resolve this discrepancy by introducing a hybrid of the Descartes method and Newton iteration, denoted ANEWDSC, which is simpler than Pan's method, but achieves a runtime comparable to it. Our algorithm computes isolating intervals for the real roots of any real squarefree polynomial, given by an oracle that provides arbitrary good approximations of the polynomial's coefficients. ANEWDSC can also be used to only isolate the roots in a given interval and to refine the isolating intervals to an arbitrary small size; it achieves near optimal complexity for the latter task.
 Publication:

arXiv eprints
 Pub Date:
 August 2013
 arXiv:
 arXiv:1308.4088
 Bibcode:
 2013arXiv1308.4088S
 Keywords:

 Computer Science  Symbolic Computation;
 Computer Science  Numerical Analysis;
 Mathematics  Numerical Analysis;
 G.1.5;
 F.2.1;
 G.1.0;
 I.1.2
 EPrint:
 to appear in the Journal of Symbolic Computation