SIGN PATTERNS OF NONNEGATIVE NORMAL MATRICES

By a nonnegative sign pattern we mean a matrix whose entries are from the set {+,0}. A nonnegative sign pattern A is said to allow normality if there is a normal matrix B whose entries have signs indicated by A . In this paper the combinatorial structure of nonnegative normal matr ices, in particular, (0, 1) normal matrices, is investigated. Among ot her results, up to order 5, (0, 1) normal matrices are classified up t o permutation similarity. A number of general conditions for sign patt erns to allow normality are obtained. Some interesting constructions o f nonnegative normal matrices are provided. In particular, a number of bordering results are obtained. Some open problems are also indicated . (C) Elsevier Science Inc., 1997.