Signum function
(Quaternion overloading of standard MATLAB® function)
Y = sign(X)
sign(X) is equivalent to unit(X). It is implemented so that MATLAB® code which calls sign will work for quaternion arrays.
>> sign(quaternion(1,2,3,4)) ans = 0.1826 + 0.3651 * I + 0.5477 * J + 0.7303 * K