Inverse cosine.
(Quaternion overloading of standard MATLAB® function)
Y = acos(X)
acos(X) computes the inverse cosine of its argument, which must be a real quaternion (acos is not yet implemented for complexified quaternions).
This function is computed using the Matlab® function of the same name by first computing an isomorphic complex number. The result is then assigned the same quaternion axis as the original argument.
>> acos(qi + qj + qk) ans = 1.571 - 0.7603 * I - 0.7603 * J - 0.7603 * K