a partial differential equation of the form Δu = f, where Δ is the Laplace operator:
When n = 3, the equation is satisfied by the potential u(x, y, z) due to a mass distribution with volume density f(x, y, z)/4π (in regions where f = 0, u satisfies the Laplace equation) and by the potential due to a charge distribution. The density of distribution f here must satisfy certain smoothness conditions—for example, continuity of the partial derivatives.
Suppose f is nonzero only in a finite region G and suppose it is bounded and has continuous first-order partial derivatives. When n = 2, the Poisson equation then has the particular solution
and when n = 3,
Here, r(A, P) is the distance between a variable point of integration A and some point P. In a more detailed form,
The solution of boundary value problems for the Poisson equation reduces, by means of the substitution u = ν + w, to the solution of boundary value problems for the Laplace equation Δw = 0. The Poisson equation was first studied by S. D. Poisson in 1812.