Primitivity of permutation groups, coherent algebras and matrices (Q1601432)

The term ``primitive'' is used in many senses in algebra. In particular, a permutation group is primitive if it preserves no non-trivial equivalence relation; a coherent algebra (such as the centralizer algebra of a permutation group) is primitive if it does not contain the matrix of such a relation; and a real square matrix is primitive if some power of the matrix has all entries strictly positive. There is a natural relationship between the first two uses of the term primitive. The main result of the present paper is the following relationship between the last two uses. A coherent algebra \(W\) has a basis consisting of square \(\{0,1\}\)-matrices. Suppose that \(W\) is not the centralizer algebra of a regular permutation group of prime degree. Then \(W\) is a primitive coherent algebra if and only if each nonidentity basis element is a primitive matrix. This result is applied to give necessary and sufficient conditions for the exponentiation \(W\uparrow G\) of a coherent algebra \(W\) by a permutation group \(G\) to be primitive.