Hi Thomas: On Thu, Dec 18, 2014 at 11:56:10AM +0100, Thomas M wrote:
I have just switched an existent project from boost 1.55.0 to 1.57.0 and my test suites diagnosed a divergence in program (a simulation) results. I have tracked down the issue to different behaviour in the normal distribution random variates generator. Below is a simple program (run under VS 2012, Update 4) that outputs random variates for a uniform and a normal distribution; comparing the output between 1.55.0 and 1.57.0 it turns out that the first bunch of uniformly distributed variates is identical, and then all others variates (both bunches of normally distributed variates as well as the second bunch of uniformly distributed variates) diverge.
Neither for 1.56.0 nor 1.57.0 does the change-log list an update to the random numbers library, so first I am puzzled why the libraries behave differently (though [Math] has undergone some changes -> propagation to [Random]?). Second, it is not clear to me why for the first bunch of uniformly distributed variates the results are identical, while for the second, after normally distributed variates were generated, the are not. It appears that the generation of normally distributed variates changes the whole state of the random numbers engine in a different manner [e.g multiple engine calls ??]. Any insight into what is going on here is much appreciated. And foremost: Is any of 1.55 or 1.57 bugged, that is one should be clearly preferred over the other?
I've observed this, too! The change seems to have been introduced in Boost version 1.56. S. -- Семен Тригубенко http://trygub.com