The nonnegative P 0 -matrix completion problem.

Abstract

In this paperthe nonnegative P 0 -matrix completion problem is considered. It is shown that a pattern for 4 × 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

=4.