  The circuit theory of mesoscopic transport provides a unified framework to
describe spin-dependent or superconductivity-related phenomena. We extend this
theory to hybrid systems of normal metals, ferromagnets and superconductors.
Our main result is an expression for the current through an arbitrary contact
between two general isotropic "nodes", which is suitable to describe the
presence of superconducting and ferromagnetic elements in the system, as well
as magnetically active interfaces/contacts. In certain cases (weak ferromagnet
and magnetic tunnel junction) we derive transparent and simple results for the
matrix current.
