quatConjugate= conj(quat)returns the complex conjugate of the quaternion,quat.

If $$q=a+b\text{i}+c\text{j}+d\text{k}$$, the complex conjugate ofqis $$q^{*}=a-b\text{i}-c\text{j}-d\text{k}$$. Considered as a rotation operator, the conjugate performs the opposite rotation. For example,

q = quaternion(deg2rad([16 45 30]),'rotvec'); a = q*conj(q); rotatepoint(a,[0,1,0])

ans = 0 1 0