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--- en:pfw:simulation-forest_fire [2023-09-04 18:18] – gelöscht - Externe Bearbeitung (Unbekanntes Datum) 127.0.0.1
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+{{pfw:banner.png}}
+===== Simulation, Forest fire =====
+This program simulates the way a forest fire develops after a lightning-strike, and it shows how the fires influence the structure of a forest. The idea is based on a publication by B. Drossel and F. Schwabl, [[https://www.sciencedirect.com/science/article/abs/pii/037843719290504J|Self-Organised critical forest-fire model]], Physical Review Letters, Vol. 69, No. 11, September 1992.
+The program functions as follows:
+The central part of the program is a toroidal grid of 512x384 bytes. Execution starts with clearing the grid, corresponding to an area without trees.
+Next an endless loop is started. In each loop the following is done:
+<code>
+Select a random cell in the grid
+Check te content if that cell
+if the content is empty
+    there is a change of 1:500 that a new tree is generated
+else
+    if the content of the cell is a tree:
+        check if any of the neighbours is a tree on fire
+            if yes -> also go on fire
+            if no -> a 1:1000000 change that 'lightning' causes fire
+        raise the age of the tree with 1 (up to 255)
+    else
+        lower the age of a fire with 1 (until 0 is reached)
+    then
+then
+update the screen for the tree or fire based on the age of the tree or          fire
+next loop
+</code>
+The program is not very fast. Executing 10.000 loops takes between 8.5 and 10.5 ms. With a grid of 512x384 and the default settings it takes about 115 million loops) before a major forest-fire develops.
+It is interesting to play around with the different settings of the program to see what happens. If you raise the chance of a lightning-strike you will see that there will be more fires, but never very big. If you raise the chance of a new tree growing there will be a high density of trees quickly, resulting in larger fires. It is also possible to raise the time it takes for a tree to catch fire from a neighbouring tree by changing the definition **(ONFIRE?)** or lowering the value **IGNITE**.
+**[[https://youtu.be/JNGmbZAHrhY|Forest fire on YouTube]]**
+{{https://user-images.githubusercontent.com/4964288/153408550-665f2bef-2022-4393-87c9-7bdef45b0746.jpg| Waldbrand2}}