ELA, Volume 9, pp. 1-20, February 2002, abstract.

The P_0-matrix completion problem

Ji Young Choi, Luz Maria DeAlba, Leslie Hogben, 
Mandi S. Maxwell, and Amy Wangsness

In this paper the P_0-matrix completion problem is
considered. It is established that every asymmetric 
partial P_0-matrix has P_0-completion. All 4-by-4 
patterns that include all diagonal positions are 
classified as either having P_0-completion or not 
having P_0-completion. It is shown that any 
positionally symmetric pattern whose graph is an 
n-cycle, with n greater than or equal to 5, has 
P_0-completion.