题目：Dual Quaternion Laplacian Matrix and Formation Control
The dual quaternion Laplacian matrix of desired relative configurations in multi-agent formation control is similar to the classical unweighted Laplacian matrix via a dual quater- nion diagonal unitary matrix. Its eigenvalues are all positive numbers except one zero eigenvalue. A unit dual quaternion vector is a desired formation vector if and only if it is in the null space of this dual quaternion Laplacian matrix. We study a control law based upon dual quaternion Laplacian. We extend our discussion to directed graphs. We also show that pairwise asymptotical stability can be reduced to rank-one asymptotical stability.