Hi John, i think your sign-function (boost/math/special_functions/sign.hpp) is incomplete. Because the resulttype is int, not all cases can be covered correctly (nan, inf, -0). With my implementation this works and it follows the std-conventions (sgn(FP) -> FP, sgn(INT/BOOL) -> double). I also tried to optimize them (branch-free, vectorizable). sgn(FP) -> FP ±0/±1 sgn(FP nan/inf) -> FP nan/inf sgn(INT) -> double +0/±1 sgn(UINT/BOOL) -> double +0/+1 regards Gero