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.