“…Recently, by the development of computer sciences, discrete and ultra-discrete versions of integral system have been attracting a great deal of attention. The ultra-discretization of soliton equations and other various important equations are intensively studied in [1,2,3,4,5,6,7,8]. Moreover, it is known that the various ultra-discrete soliton equations are obtained from solvable vertex model in statistical mechanics in a certain limiting procedure [9,10].…”