Differential Equation/Examples/Second Order Linear Partial 1

Example of Differential Equation
Partial non-linear differential equation of the $2$nd order in $3$ independent variables:
 * $\dfrac {\partial^2 V} {\partial x^2} + \dfrac {\partial^2 V} {\partial y^2} + \dfrac {\partial^2 V} {\partial z^2} = 0$