APPROXIMATION OF PERIODIC FUNCTIONS BY STEKLOV AVERAGES IN L_2

摘要

In the space L_2 of periodic functions, we establish exact (in the sense of constants) estimates from below for the deviation of the Steklov functions of the first and second order in terms of the modulus of continuity of the second order. Similar results are also established for even continuous periodic functions with nonnegative Fourier coefficients in the space C. Bibliography. 5 titles.