Recent attention in the study of sign pattern matrices is the characterization of sign pattern matrices that require algebraic positivity and the characterization of sign pattern matrices that allow algebraic positivity.In this book we study the conditions for sign pattern matrices of order 2 and 3 to allow algebraic positivity, and apply them to the sign controllability of linear control systems.We first give a necessary condition for sign pattern matrices to allow algebraic positivity and, based on this fact, characterize all spectrally arbitrary sign pattern matrices that allow algebraic...