A Characterization of Minimal Semipositivity of Sign Pattern Matrices

A real m n matrix A is semipositive (SP) if there is a vector x 0 such that Ax > 0, inequalities being entrywise. A is minimally semipositive (MSP) i f A is semipositive and no column deleted submatrix of A is semipositive. We give a necessary and suucient condition for the sign pattern matrix with n positive e n tries to be minimally semipositive.