Schwinger variational principle for bound states and scattering problems

Schwinger variational principle (SVP) is formulated for the two-body problem and the theory of multichannel scattering for the mass shell and the off-mass shell amplitudes on the basis of the equivalence of the separabilization method and variational principle. Detailed investigation of the SVP for discrete spectrum problems is presented here for the first time probably. Corrections to the basic approximation of the byperspherical function method are studied.