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Advances in the VAS CF method using better bounds
Alkiviadis G. AkritasDepartment of Computer & Communication Engineering
University of ThessalyVolos, Greece
(joint work with Strzebonski and Vigklas)
CASC 2007, Bonn, Germany 2
Outline of the talk
Presentation of two methods derived from Vincent’s theorem.
Better estimations of upper bounds on the positive roots of polynomials.
Tables showing improvement of the VAS CF real root isolation method.
CASC 2007, Bonn, Germany 3
The rule of signs var(p): exact only if var(p) = 0 or 1
CASC 2007, Bonn, Germany 4
Vincent’s theorem (1836)(Continued Fractions Version)
CASC 2007, Bonn, Germany 5
Real Root Isolation
CASC 2007, Bonn, Germany 6
Most Important Observation
CASC 2007, Bonn, Germany 7
VAS – continued fractionsmethod (uses Descartes’ test)
CASC 2007, Bonn, Germany 8
Vincent’s theorem (2000)(Alesina-Galuzzi: Bisection)
CASC 2007, Bonn, Germany 9
Vincent’s Termination Test
CASC 2007, Bonn, Germany 10
Uspensky’s Termination Test(special case of Vincent’s test)
CASC 2007, Bonn, Germany 11
Termination test named after Uspensky because:
Uspensky was the one to use it as a test, since he was not aware of Budan’s theorem.
CASC 2007, Bonn, Germany 12
Budan’s theorem(from Vincent’s paper of 1836)
CASC 2007, Bonn, Germany 13
Vincent vs Uspensky
CASC 2007, Bonn, Germany 14
The VCA algorithm ---original version
CASC 2007, Bonn, Germany 15
REL: Fastest implementation of VCA bisection method
CASC 2007, Bonn, Germany 16
Comparison times using Cauchy’s rule in VAS CF
CASC 2007, Bonn, Germany 17
Stefanescu’s theorem (2005)
CASC 2007, Bonn, Germany 18
Matching coefficients plus breaking up coefficients
Stefanescu introduced the concept of matching (or pairing) a positive coefficient with a negative one of lower degree.We introduced the concept of breaking up a positive coefficient --- into parts to be matched with negative coefficients.
(for ANY number of sign variations!)
CASC 2007, Bonn, Germany 19
Our theorem (1/2)
CASC 2007, Bonn, Germany 20
Our theorem(2/2)
CASC 2007, Bonn, Germany 21
Problems with a single method of computing bounds
CASC 2007, Bonn, Germany 22
Use two methods to compute the bound; pick the minimum
CASC 2007, Bonn, Germany 23
CASC 2007, Bonn, Germany 24
Comparison times using new bounds in VAS CF
CASC 2007, Bonn, Germany 25
Conclusions
CASC 2007, Bonn, Germany 26
References I
CASC 2007, Bonn, Germany 27
References II