Main Article Content
In this paperthe nonnegative P0-matrix completion problem is considered. It is
shown that a pattern for 4 × 4 matrices that includes all diagonal positions has nonnegative P0-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 P0-completion if and only if n = 4.