Kolmogorov widths of balls in mixed norms: the case of rigidity

Yuri Malykhin, Konstantin Ryutin

We describe the set of parameters $(p_1,p_2,q_1,q_2)$ such that the balls $B_{q_1,q_2}^{s,b}$ are rigid in ${\ell }_{q_1,q_2}^{s,b}$ metric i.e. they are poorly approximated by linear…