Let R be the set of nonnegative matrices whose row and column sums fall between specific limits and whose entries sum to some fixed h > 0. Closely related axiomatic approaches have been developed to ascribe meanings to the statements: the real matrix fe R and the integer matrix a ~ R are "proportional to" a given matrix p ~> 0. These approaches are described, conditions under which proportional solutions exist are characterized, and algorithms are given for finding proportional solutions in each case.