@article{Vakarchuk_2012, title={Best mean-square approximation of functions defined on the real axis by entire functions of exponential type}, volume={64}, url={https://umj.imath.kiev.ua/index.php/umj/article/view/2601}, abstractNote={Exact constants in Jackson-type inequalities are calculated in the space $L_2 (\mathbb{R})$ in the case where the quantity of the best
approximation $\mathcal{A}_{\sigma}(f)$ is estimated from above by the averaged smoothness characteristic $\Phi_2(f, t) = \cfrac 1t \int^t_0||\Delta^2_h(f)||dh$.
We also calculate the exact values of the average $
u$-widths of classes of functions defined by $\Phi_2$.}, number={5}, journal={Ukrainsâ€™kyi Matematychnyi Zhurnal}, author={Vakarchuk, S. B.}, year={2012}, month={May}, pages={604-615} }