Block Kronecker ansatz spaces for matrix polynomials

In this paper, we introduce a new family of equations for matrix pencils that may be utilized for the construction of strong linearizations for any square or rectangular matrix polynomial. We provide a comprehensive characterization of the resulting vector spaces and show that almost every matrix pencil therein is a strong linearization regardless whether the matrix polynomial under consideration is regular or singular. These novel “ansatz spaces” cover all block Kronecker pencils as introduced in [6] as a subset and therefore contain all Fiedler pencils modulo permutations. The important case of square matrix polynomials is examined in greater depth. We prove that the intersection of any number of block Kronecker ansatz spaces is never empty and construct large subspaces of block-symmetric matrix pencils among which still almost every pencil is a strong linearization. Moreover, we show that the original ansatz spaces L1 and L2 may essentially be recovered from block Kronecker ansatz spaces via pre- and postmultiplication, respectively, of certain constant matrices.