. "First, the first term on the right side of the equation (8) is approximated from the following equation (1) or (14). ##EQU4## where, E represents an element including the nodes Ni and Nj and k is a node number of a node other than those of the nodes Ni and Nj and belonging to the element E. Ti, Tj, and Tk denote values of the function T at the nodes Ni, Nj, and Nk respectively." . . .