Extremal copositive matrices with minimal zero supports of cardinality two.

Let <inline-graphic></inline-graphic> be an extremal copositive matrix with unit diagonal. Then the minimal zeros of A all have supports of cardinality two if and only if the elements of A are all from the set <inline-graphic></inline-graphic>. Thus the extremal copositive matrices with minimal zero supports of cardinality two are exactly those matrices which can be obtained by diagonal scaling from the extremal <inline-graphic></inline-graphic> unit diagonal matrices characterized by [Hoffman, Pereira, 1973]. [ABSTRACT FROM AUTHOR]