Two elastic disks, a and b, bouncing in a square : a variant of the gas of Szilard.
The initial conditions are clearly apparent from the following figure (Arbitrary units) :
Time evolution : each collision (one wall or the other disk) is named an “event” (9 possibilities). Events are labeled by integer j. Multiple collisions are forbidden (The program halts prematurely). Cible[j] is an integer (∈{1,...,9}) memorizing the type of event.
Checking the conservation of energy :
50000 events have been calculated, 36 are displayed here :
Histogram of the kinetic energy ratio, 
: the maximum corresponds to the equipartition.
Mean time between two collisions (a and b) :
