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Exact Kolmogorov-Type Inequalities with Bounded Leading Derivative in the Case of Low Smoothness
Authors:Babenko  V. F.  Kofanov  V. A.  Pichugov  S. A.
Affiliation:(1) Dnepropetrovsk University, Dnepropetrovsk
Abstract:We obtain new unimprovable Kolmogorov-type inequalities for differentiable periodic functions. In particular, we prove that, for r = 2, k = 1 or r = 3, k = 1, 2 and arbitrary q, p isin [1, infin], the following unimprovable inequality holds for functions 
$$x in L_infty ^r $$
:

$$left| {x^{left( k right)} } right|_q  leqslant frac{{left| {{phi }_{r - k} } right|_q }}{{left| {{phi }_r } right|_p^alpha  }}left| x right|_p^alpha  left| {x^{left( k right)} } right|_infty ^{1 - alpha } $$
where 
$$alpha = min left{ {1 - frac{k}{r},frac{{r - k + {1 mathord{left/ {vphantom {1 q}} right. kern-nulldelimiterspace} q}}}{{r + {1 mathord{left/ {vphantom {1 p}} right. kern-nulldelimiterspace} p}}}} right}$$
and phivr is the perfect Euler spline of order r.
Keywords:
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