Logarithmic Derivatives of Least Deviation from Zero

Abstract

We study least deviation of logarithmic derivatives of real-valued polynomials with a fixed root from zero on the segment $[-1;1]$ in the uniform norm with the weight $\sqrt{1-x^2}$ and without it. Basing on results of Komarov and Novak and on a certain determinant identity due to Borchardt, we also establish a criterion for best uniform approximation of continuous real-valued functions by logarithmic derivatives in terms of a Chebyshev alternance.