We prove that max t∈ [−π,π] |Q(t)| ≤ T 2n (sec(s/4)) = 1 2 ((sec(s/4) + tan(s/4)) 2n + (sec(s/4) − tan(s/4)) 2n ) for every even trigonometric polynomial Q of degree at most n with complex coefficients satisfyingwhere m(A) denotes the Lebesgue measure of a measurable set A ⊂ R and T 2n is the Chebysev polynomial of degree 2n on [−1, 1] defined by T 2n (cos t) = cos(2nt) for t ∈ R. This inequality is sharp. We also prove that max t∈[−π,π] |Q(t)| ≤ T 2n (sec(s/2)) = 1 2 ((sec(s/2) + tan(s/2)) 2n + (sec(s/2) − tan(s/2)) 2n )for every trigonometric polynomial Q of degree at most n with complex coefficients satisfying
ForewordI started my Ph.D. program in June, 1987, at The Ohio State University, as a student of Paul Nevai. In August, 1987, Paul Nevai moved from Columbus, Ohio, to Columbia, South Carolina, to spend the school year 1987-88 at the University of South Carolina, and each of his students followed him. This is how I met Mr. (Yingkang) Hu, who was a student of Ron DeVore at that time. It was a somewhat short but very exciting time for me at the University of South Carolina. Not only had I passed each of my necessary exams in my Ph.D. program but I had the possibility to learn from and interact with some of the very best researchers in approximation theory. My office neighbors were Paul Nevai, Ron DeVore, and George Lorenz. George Lorentz happened to be Ron DeVore's Key words and phrases. trigonometric polynomials, Remez-type inequalities, geometry of polynomials.