A second-order Partial Differential Equation arising in physics:

If , it reduces Laplace's Equation. It is also related to the Helmholtz Differential Equation

**References**

Arfken, G. ``Gauss's Law, Poisson's Equation.'' §1.14 in
*Mathematical Methods for Physicists, 3rd ed.* Orlando, FL: Academic Press, pp. 74-78, 1985.

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1999-05-25