Note on an ambiguous case of approximation
Dunham Jackson · Transactions of the American Mathematical Society · 1923
Introduction.Let f(x) be a continuous function of period 2 n.The writer has discussed to some extent the existence and properties of a trigonometric sum Tmn(x), of order n at most, determined by the condition that * Presented to the Society, December 30, 1920.f See D.Jackson, On functions of closest approximation, these Transactions, vol.22 (1921), pp.117-128; Note on a class of polynomials of approximation, these Transactions, vol.22 (1921), pp.320-326; On the convergence of certain trigonometric and polynomial approximations, these Transactions, vol.22 (1921), pp.158-166.These papers will be referred to by the letters A, B, C, respectively.