A look-ahead block schur algorithm for diagonal plus semiseparable matrices

A look-ahead recursive algorithm for the block triangular factorization of matrices represented as a sum of diagonal and semiseparable ones is derived. This factorization is used for fast solving of the corresponding linear system. For the case of sizes of diagonal blocks not depending on dimension of original matrix, the algorithm obtained has linear complexity. For a wide class of matrices, the algorithm exhibits stable behavior.