Approximative properties of diagonal operators in Orlicz spaces
  We obtain the exact values of some important approximative quantities (such as, the best approximation, the basis width, Kolmogorov's width and the best $n$-term approximation) of certain sets of images of the diagonal operators in the Orlicz sequence spaces $l_M$. 
Andriy L. Shidlich, Stanislav O. Chaichenko
math.NA