“…As a result, there are several formulations of CBS that appear unrelated at a quick inspection. Concrete examples of these formulations include the transfer or companion matrices [28-30, 33, 35, 42, 56, 66, 72, 73, 76, 82, 86, 89, 101, 104, 121, 140, 148-154], the propagation matrix [11,16,23], bivariational methods [155], wavefunction matching techniques [2,7,9,38,39,44,81,88], and Green function-based approaches [24,26,27,34,41,43,134,156,157]. Note that these terms are very broad; e.g., several different "transfer matrices" have been reported.…”