id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
8837	boost::math::students_t quantile() fails for huge degrees of freedom	Paul McClellan <paulm@…>	John Maddock	"Student's t quantile function calls policies::raise_rounding_error() in iround() when degrees of freedom = 4503599627370496.

boost::math::students_t students(4503599627370496);
double dRes = quantile(students, 0.4);

If this is disabled using
#define BOOST_MATH_ROUNDING_ERROR_POLICY ignore_error
in user.hpp the computation will continue.

The function inverse_students_t_hill() uses the test ndf > 1e20 to use the Standard Normal approximation, but Boost subsequently attempts to refine the estimate using the Halley step in fast_students_t_quantile_imp() and this becomes unreliable and eventually fails for huge dof such as dof = DBL_MAX (results in completely wrong result) or +Infinity (returns a NaN).

For consistency, I suggest the quantile function us the same threshold as pdf() and cdf() to approximate the Student's t with the standard normal distribution when dof > 1/eps.

I will attempt to attach my user.hpp file."	Bugs	closed	To Be Determined	math	Boost 1.54.0	Problem	fixed	math