Sun Yongsheng.A REMARK ON KOLMOGOROVS COMPARISON THEOREM[J].Chinese Annals of Mathematics B,1987,8(4):463~467
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Authors：
Sun Yongsheng;
Abstract：
In approximation theory the theorem of Kolmogorov concerning the comparison of derivatives of differentiable functions defined on the real line is well—known. It plays an important role in establishing sharp inequalities between the norms of derivatives of a function. In this note we establish a comparison theorem of Kolmogorov type on a class of functions which are defined on the real line and can be contlnuated analytically in a stripped region containing the real line. As a consequence we have derived an inequality of Landau-Kolmogorov type on this function class, and moreover, we have applied it to get the exact estimation for the Kolmogorov's N-widths of the analytic function class.
