Seonglae ChoDirichlet condition
Convergence of Fourier series
In mathematics, the question of whether the Fourier series of a periodic function converges to a given function is researched by a field known as classical harmonic analysis, a branch of pure mathematics. Convergence is not necessarily given in the general case, and certain criteria must be met for convergence to occur.
https://en.wikipedia.org/wiki/Convergence_of_Fourier_series#Convergence_at_a_given_point
Dirichlet–Jordan test
In mathematics, the Dirichlet–Jordan test gives sufficient conditions for a real-valued, periodic function f to be equal to the sum of its Fourier series at a point of continuity. Moreover, the behavior of the Fourier series at points of discontinuity is determined as well (it is the midpoint of the values of the discontinuity). It is one of many conditions for the convergence of Fourier series.
https://en.wikipedia.org/wiki/Dirichlet–Jordan_test