The Stratonovich Formulation of Quantum Feedback Network Rules
  We express the rules for forming quantum feedback networks using the Stratonovich form of quantum stochastic calculus rather than the Ito, or SLH form. Remarkably the feedback reduction rule implies that we obtain the Schur complement of the matrix of Stratonovich coupling operators where we short out the internal input/output coefficients. 
J.E. Gough
quant-ph math-ph math.MP