[Boost-users] Box-Muller - normal distributed random numbers

Hi, I wonder why _cached_rho is calclulated this way: sqrt(-result_type(2) * log(result_type(1)-_r2)); in normal_distribution.hpp:70 and not sqrt(-result_type(2) * log(_r2)); So I don't understand why there is "result_type(1) - _r2" instead of just "_r2". Cheers! matthias PS.: I hope this was not a stupid question, if so please forgive me as I am just a newbie.