ELA, Volume 10, pp. 46-59, March 2003, abstract.
The nonnegative P_0-matrix completion problem
Ji Young Choi, Luz Maria DeAlba, Leslie Hogben,
Benard M. Kivunge, Sandra K. Nordstrom, and
Mike Shedenhelm
In this paper the nonnegative P_0-matrix completion
problem is considered. It is shown that a pattern for
4-by-4 matrices that includes all diagonal positions
has nonnegative P_0-completion if and only if its
digraph is complete when it has a 4-cycle. It is also
shown that any positionally symmetric pattern that
includes all diagonal positions and whose graph is an
n-cycle has nonnegative P_0-completion if and only
if n is not equal to 4.