  In the standard minority game, every agent switches to his best strategy in
hand at each time step. If only a small number of agents are allowed to switch
their strategies at each time step, the population variance of the system
plunges. The variance reaches a low value and remains steady for a period of
time. Then without any sign it starts to rise abruptly to a high value and then
decreases smoothly to the previous low value again. The process of an abrupt
rise followed by a gentle decrease repeats again and again but without obvious
characteristic length as time goes on. The phenomenon is similar to the
collapse of a sand pile with sands being added continuously from the top. We
define the scale of collapse of the population variance by the difference of
the variance before and after an abrupt rise. We then find that the logarithmic
plot of the frequency versus scale of the collapses follows a power law.
