The variational method proposed by KadanoF et at. is very useful for solving various statistical models.
However, there are two major diFiculties. Its numerical procedure is tedious and tiine consuming, and the
authors considered that there exists an "internal contradiction. " We have resolved both of them by
developing a new variational procedure, and examining the physical meaning of the variational parameters.
Physical Review B (Condensed Matter) 19(1), pp.529-532