Nonunital decompositions of the matrix algebra of order three

Abstract

All decompositions of $M_3(\mathbb{C})$ into a direct vector-space sum of two subalgebras such that none of the subalgebras contains the identity matrix are classified. Thus, the classification of all decompositions of $M_3(\mathbb{C})$ into a direct vector-space sum of two subalgebras as well as description of Rota-Baxter operators of nonzero weight on $M_3(\mathbb{C})$ is finished.