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[Václav Šmilauer <eu@xxxxxxxx>]

Hi there,

I updated scripts/test/energy.py in r2546; it is a simple simulation of 
many balls falling on plane in gravity. There are contributions of 
gravity work, elastic potential, plastic dissipation, kinetic energy and 
non-viscous damping (if enabled). If the script is run, the total is not 
zero, as if more energy were dissipated then put into the system. The 
value of the total does not seem to depend on dt. If damping is 
non-zero, it is much lower (almost zero for 0.2, for instance).

I am not sure about the cause; two possible explanations come to mind 
(i) mid-step values of velocity vs. on-step accelerations etc. and (ii) 
without damping, many elastic collisions take place (their number 
increases if damping is small, as the system never goes to quasi-static 
state) and integration error accumulates (what contradicts this is that 
the precision would be increased with smaller dt, which is not the case, 
and also that the imprecision effects would cancel each other in average).

Could someone have a look at the code and suggest something?

Cheers, Vaclav