Isotropic Diffusion (Heat Equation)

Formal definition:

In mathematics, if given an open subset U of R^n (R^2 in this case) and a subinterval 
I of R, one says that a function u : U × I → R is a solution of the heat equation if

Using Finite Differences:

By combining different Taylor series expansions, we can obtain approximations of the 
first and second derivatives

Substituting in the original equation we get the discrete form of the Heat Equation

Where: