For given Z, B is an element of C-nxk, the problem of finding Lambda is an element of C-nxn, in some prescribed class W, that minimizes parallel to AZ - B parallel to (Frobenius norm) has been considered by different authors for distinct classes W. Here, this minimization problem is studied for two other classes, which include the symmetric Hamiltonian, symmetric skew-Hamiltonian, real orthogonal symplectic and unitary conjugate symplectic matrices. The problem of minimizing parallel to A - (A) over tilde parallel to, where (A) over tilde is given and A is a solution of the previous problem, i...
