Rules:
1. x_ij empty == (a) ==> tree
2. x_ij tree == (p / lightning) ==> fire
3. x_ij tree == (fire / neighbor) ==> fire
4. x_ij fire == ==> empty
5. x_ij not triggered ==> same status
Example implementation with 2 matrices: now and then
1. zero out then
2. walk through now and populate then
3. copy then to now