The special unitary group SU_n(q) is the set of n×n unitary matrices with determinant +1 (having n^2 - 1 independent parameters). SU(2) is homeomorphic with the orthogonal group O_3^+(2). It is also called the unitary unimodular group and is a Lie group. Special unitary groups can be represented by matrices U(a, b) = [a | b -b^_ | a^_], where a^_ a + b^_ b = 1 and a, b are the Cayley-Klein parameters.