The extreme rays of several
cones of complex and real diagonally dominant matrices, and their duals, are
identified. Several results on lattices of faces of cones are given. It is then shown that
the dual (in the real space of hermitian matrices) of the cone of hermitian
diagonally dominant matrices cannot be the image of the cone of positive
semidefinite matrices under any nonsingular linear transformation; in particular, it
cannot be the image of the cone of positive semidefinite matrices under the
Ljapunov transformation H↦AH + HA∗ determined by a positive stable matrix
A.