A simple model of diffusion in a 1 dimensional strip x_{t}(i)
is as follows
x_{t+1}(i) =
D x_{t}(i1) +
(1  2 D) x_{t}(i) +
D x_{t}(i+1)
This gives the value at element i at time t+1
where D is the coefficient of diffusion, normally 0 < D << 1.
As an example, consider how a single point diffuses in time. In the following
image time runs down the screen.
