The two-dimensional **Laplace equation** is a second-order partial differential equation (PDE) that describes the behavior of scalar fields like electrostatic potentials or temperature distributions in two dimensions. It is a special case of the Poisson equation when the source term is zero.
The general form of the two-dimensional Laplace equation is:
\[
\frac{\partial^2 \phi}{\partial x^2} + \frac{\partial^2 \phi}{\partial y^2} = 0
\]
where:
- \(\phi(x, y)\) is the unknown scalar field (e.g., potential or temperature),
- \(\frac{\partial^2 \phi}{\partial x^2}\) is the second partial derivative of \(\phi\) with respect to \(x\),
- \(\frac{\partial^2 \phi}{\partial y^2}\) is the second partial derivative of \(\phi\) with respect to \(y\).
In words, this equation states that the sum of the second derivatives of \(\phi\) in both the \(x\)- and \(y\)-directions must equal zero for the field to be in equilibrium (i.e., harmonic).
This equation appears frequently in physics and engineering, especially in problems involving steady-state heat conduction, electrostatics, and incompressible fluid flow.