Strong forms of nonsingularity

Abstract Motivated by certain views of the sign nonsingular matrices, we begin study of several classes of nonsingular matrices naturally intermediate between sign nonsingular matrices and the ordinary nonsingular matrices. These all involve Hadamard products that allow constrained changes in the magnitudes (but not the signs) of entries, or the selection of patterns of subblocks. Among a wide variety of results is the fact that the nonsingular matrices A for which A·A -1 T is doubly stochastic arise as one of our “strong” forms of nonsingularity.