On the positive stability of $P^2$-matrices
  In this paper, we study the positive stability of $P$-matrices. We prove that a $P$-matrix A is positively stable if A is a $Q^2$-matrix and there is at least one nested sequence of principal submatrices of A each of which is also a $Q^2$-matrix. This result generalizes the result by Carlson which shows the positive stability of sign-symmetric $P$-matrices and the result by Tang, Simsek, Ozdaglar and Acemoglu which shows the positive stability of strictly row (column) square diagonally dominant for every order of minors $P$-matrices. 
Olga Y. Kushel
math.SP