关于函数类Ω_P~(r+1)[0,1]的宽度估计

§1.引言设l≥1,r=2l,t_1,…,t_l≥0,D=(d/dx),I为恒等算子,记Q_(r+1)(D)=D(D~2-f_j~2I),q_r(x)=(x~2-f_j~2),Ω_p~(r+1)[0,1]={f(x);f~(r)在[0,1]上绝对连续,且‖Q_(r+1)(D)f(·)‖p≤1,f~(2k-1)(0)=f~(2k-1)(1)=0,k=1,…,l},(1.1)于是,f∈Ω_p~(r+1)[0,1],当且仅当