The Lebesgue constant for the periodic Franklin system
We identify the torus with the unit interval [0,1) and let n,ν ∈ ℕ with 0 ≤ ν ≤ n-1 and N:= n+ν. Then we define the (partially equally spaced) knots = ⎧ j/(2n) for j = 0,…,2ν, ⎨ ⎩ (j-ν)/n for for j = 2ν+1,…,N-1. Furthermore, given n,ν we let be the space of piecewise linear continuous functions on the torus with knots . Finally, let be the orthogonal projection operator from L²([0,1)) onto . The main result is . This shows in particular that the Lebesgue constant of the classical Franklin...