Hi, you forgot the WINAPI in front of the function declaration and implementation. Maybe you should add a set_mat(_11, _12, _13, ....) macro to make the exp_mat better to read and not that big in size, However, I think it's better to dynamically calculate the expected matrix rather than compare it to hard-coded values (I'm not sure about that one though, it's just what _I_ would do). It would at least make the whole thing easier be adopted to new tests (of the same function with different values). Best regards, Tony