TY - JOUR

T1 - Counterexamples to Tischler's strong form of smale's mean value conjecture

AU - Tyson, Jeremy T.

N1 - Funding Information:
Received 14 February 2003; revised 7 November 2003. 2000 Mathematics Subject Classification 30C15. Research supported by the U.S. National Science Foundation under Grant DMS-0228807.

PY - 2005

Y1 - 2005

N2 - Smale's mean value conjecture asserts that minθ |P(θ)/θ| ≤ K|P′(0)| for every polynomial P of degree d satisfying P(0) = 0, where K = (d-1)/d and the minimum is taken over all critical points 6 of P. A stronger conjecture due to Tischler asserts that minθ|1/2 - P(θ)/θ·P′(0)| ≤ K 1 with K1 = 1/2 - 1/d. Tischler's conjecture is known to be true: (i) for local perturbations of the extremum P0(z) = z d - dz, and (ii) for all polynomials of degree d ≤ 4. In this paper, Tischler's conjecture is verified for all local perturbations of the extremum P1(z) = (z - 1)d -(-1)d, but counterexamples to the conjecture are given in each degree d ≥ 5. In addition, estimates for certain weighted L1- and L 2-averages of the quantities 1/2 - P(θ)/θ · P′(0) are established, which lead to the best currently known value for K1 in the case d = 5.

AB - Smale's mean value conjecture asserts that minθ |P(θ)/θ| ≤ K|P′(0)| for every polynomial P of degree d satisfying P(0) = 0, where K = (d-1)/d and the minimum is taken over all critical points 6 of P. A stronger conjecture due to Tischler asserts that minθ|1/2 - P(θ)/θ·P′(0)| ≤ K 1 with K1 = 1/2 - 1/d. Tischler's conjecture is known to be true: (i) for local perturbations of the extremum P0(z) = z d - dz, and (ii) for all polynomials of degree d ≤ 4. In this paper, Tischler's conjecture is verified for all local perturbations of the extremum P1(z) = (z - 1)d -(-1)d, but counterexamples to the conjecture are given in each degree d ≥ 5. In addition, estimates for certain weighted L1- and L 2-averages of the quantities 1/2 - P(θ)/θ · P′(0) are established, which lead to the best currently known value for K1 in the case d = 5.

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U2 - 10.1112/S0024609304003613

DO - 10.1112/S0024609304003613

M3 - Article

AN - SCOPUS:29744434752

VL - 37

SP - 95

EP - 106

JO - Bulletin of the London Mathematical Society

JF - Bulletin of the London Mathematical Society

SN - 0024-6093

IS - 1

ER -