This Demonstration shows the contagion effect inherent in a spreading fire. The focus is not so much on the complex movement of the fire as on its spread, given an individual tree's wetness percentage. The power of rule-based recursion and injected randomness are used to achieve the contagion effect. Red cells are burning and black cells are burned; the total burn area is the sum of the red and black cells.
The computation is performed by a search-update-feedback cellular automaton (SCA). The rule implemented simply requires that a tree be set ablaze if a single neighboring tree is burning; the burn neighborhood consists of nine trees, including the current tree location.
The control "fire spread model" triggers the SCA and maintains an expanding fire. Set the "side of tree grid" control before triggering. Pause, and toggle "new initial burn location" to restart at a desired new initial burn location, then uncheck this control before retriggering, or use this control at any time without pausing and toggle the initial burn location to a new location. Slide the "tree wetness percentage" control at any time to simulate tree wetness. Toggle the "matrix plot or network" control at any time to switch between the matrix plot view and the network view.