\begin{thebibliography}{1}

\bibitem{berman94}
A.~Berman and R.~J. Plemmons, {\em Nonnegative Matrices in the Mathematical
  Sciences}.
\newblock Classics in Applied Mathematics Series, Philadelphia: {SIAM}, 1994.

\bibitem{fiedler62}
M.~Fiedler and V.~Pt\'{a}k, ``On matrices with non-positive off-diagonal
  elements and positive principal minors,'' {\em Czechoslovak Journal of
  Mathematics}, vol.~12, no.~87, pp.~382--400, 1962.

\end{thebibliography}
