Fourier series

In mathematics, the Fourier series, named after Joseph Fourier (1768—1830), of a complex-valued periodic function f of a real variable, is an infinite series

$\sum _{n=-\infty }^{\infty }c_{n}e^{2\pi inx/T}$

defined by

$c_{n}={\frac {1}{T}}\int _{0}^{T}f(x)\exp \left({\frac {-2\pi nx}{T}}\right)\,dx.$

In what sense it may be said that this series converges to f(x) is a somewhat delicate question.