CP rank of completely positive matrices of order 5 Original Research Article

J.H. Drew et al. [Linear and Multilinear Algebra 37 (1994) 304] conjectured that for ngreater-or-equal, slanted4, the completely positive (CP) rank of every n×n completely positive matrix is at most [n2/4]. In this paper we prove that the CP rank of a 5×5 completely positive matrix which has at least one zero entry is at most 6, thus providing new supporting evidence for the conjecture.