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## The Burn Simulation

### News

2006/02/11: Version 1.0
Fixing some build problems with older versions.
2003/10/14: Version 0.99
Initial public release of the fast burn simulation.

### The Simulation

The simulation itself is pretty easy to understand: The forest is an area of cells, each cell representing a tree or empty space. A tree is characterized by the following variables:

• The state: It can either be living (displayed green), burning (red color) or dead (color black).
• The mass: Initially, the tree has some user-specified mass; while it is burning the mass is decreasing until it reaches 0 and the tree is finally dead.

The empty space (i.e. cells which are no trees) are displayed white.

You now do the following: Decide on a tree density; a value between 0 and 1 which represents the ratio of trees among all cells (all other cells stay empty). Then, set fire ("ignite") some of the trees (by clicking on them with the mouse in QXBurn or using the auto-ignition). Then start the sim and watch what happens:
The sburning trees will burn a number of time ticks (depending on their mass) and may set fire on neighboring trees as long as they burn. There are 8 neighbours for each tree and the ignition probability per time tick can be adjusted in two ways: Either by specifying a wind force, direction and forest combustibility or by directly entering percent values.

### What you will see...

You will notice that there is a certain tree density called the critical tree density. If there are fewer trees, only very few of them will burn no matter how many you initially ignite. If you are above the critical density, (nearly) the complete forest will go up in flames even if you initially set fire on just a few trees.

### QXBurn

What was described above is what you can do with QXBurn. Change the tree density just a little, run the sim again, change the density, run again, etc. will give you a feeling for the critical density. You can do that fairly quickly using auto-ignition, see the program page for QXBurn for details and a screen shot.
But what about having a graph showing the percentage of burnt trees in relation to the tree density...?

### STBurn

...That is what STBurn is for. You cannot see the forest burning, you just get the results presented. Check out the program page for STBurn for details and a screen shot.