GENERALIZED CHANDRASEKHAR RECURSIONS FROM THE GENERALIZED SCHUR-ALGORITHM

We present a new approach to the Chandrasekhar recursions and some gen eralizations thereof. The derivation uses the generalized Schur recurs ions, which are O(N-2) recursions for the triangular factorization of NxN matrices having a certain Toeplitz-like displacement structure. It is shown that when the extra structure provided by an underlying stat e-space model is properly incorporated into the generalized Schur algo rithm, it reduces to the Chandrasekhar recursions, which are O(Nn(2)) recursions for estimating the n-dimensional state of a time-invariant (or constant-parameter) system from N measured outputs. It is further noted that the generalized Schur algorithm factors more general struct ured matrices, and this fact is readily used to extend the Chandrasekh ar recursions to a class of time-variant state-space models, special c ases of which often arise in adaptive filtering.