بوتار ِ دیریکله
Fr.: condition de Dirichlet
One of the following conditions for a → Fourier series
1) The function f(x) is defined and single valued, except possibly at a finite number of
points in the interval -π, +π.
2) f(x) has a period of 2π.
3) f(x) and f'(x) are
→ piecewise continuous functions on -π, +π.
Then, the Fourier series converges to:
(a) f(x) if x is a point of continuity.
(b) (f(x + 0) + f(x - 0))/2, if x is a point of discontinuity.
Named after Peter Gustav Lejeune Dirichlet (1805-1859), German mathematician who
made valuable contributions to → number theory,
→ analysis, and → mechanics;