In mathematics, the Fejér kernel is a summability kernel used to express the effect of Cesàro summation on Fourier series. It is a non-negative kernel, giving rise to an approximate identity. It is named after the Hungarian mathematician Lipót Fejér (1880–1959). The Fejér kernel has many equivalent definitions. We outline three such definitions below:
Michaël Unser, Daniel Sage, Kunal Narayan Chaudhury