Sign-nonsingular skew-symmetric matrices Original Research Article

Sign-nonsingular skew-symmetric matrices are investigated. The concept of a nonsingular graph is introduced, and such graphs are related to pfaffian graphs. Considerable attention is devoted to properties of sign-nonsingular skew-symmetric matrices A = (aij) for which there do not exist sign-nonsingular skew-symmetric matrices B = (bij) of the same order with more nonzero entries and aij = 0 whenever bij = 0.