Computing Electric field of a double dipole by solving Poisson's Equation

This code computes the E-fields due to 2-dipoles in a 2-D plane using Finite difference method.

In this code, the boundary condition for the Poisson equation are known potentials 100V and -100 V alternatively, along the 4 end walls. Two identical dipoles with charges 2nC are placed at x=10 and x=-10. Poisson equation is iteratively solved using the Finite difference method (FDM).
The solution of the Poisson equation is plotted as the electric potential contours. Electric field is computed using gradient function, and is also shown as quiver plot.