BernsteinType Inequalities for Linear Combinations of Shifted Gaussians
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abstract
Let Pn be the collection of all polynomials of degree at most n with real coefficients. A subtle Bernstein-type extremal problem is solved by establishing the inequality Un(m)| Lq() (c1+1/qm)m/2 n m/2UnLq() for all U n Gn, q (0, ], and m = 1, 2,..., where c is an absolute constant and Gn := {f : f(t) = j=1N Pmj (t)e-(t-j)2, j , Pmj, j=1N (mj + 1) n}. Some related inequalities and direct and inverse theorems about the approximation by elements of Gn in Lq() are also discussed. 2006 London Mathematical Society.