Develop a computer program using python to model diffusion limited aggregation, or DLA for short. Take a square grid (101x101) with a single particle in the middle. For this simulation, the particle will be restricted to moving up, down, left, or right. The particle performs a random walk until it reaches a point on the edge of the square, at which point it sticks to the edge, becoming immoveable. Then, a second particle starts at the center and does a random walk until it sticks to either a particle or a an edge. A third particle then starts at the center, and the process continues until a particle cannot move from its initial position. Repeat this with a 201x201 lattice.