Two-dimensional Lattice Example about gutzwillerdynamics HOT 3 OPEN

            for i_site in range(self.N_sites):
                self.i2xy(i_site, xy)
                x = xy[0]
                y = xy[1]
                self.site_coords[i_site, :] = xy[:]
                # Case 1: Periodic boundary conditions (PBC):
                if self.OBC == 0:
                    self.N_nbr[i_site] = 4
                    self.nbr[i_site, 0] = self.xy2i((x - 1 + self.L) % self.L, y)
                    self.nbr[i_site, 1] = self.xy2i(x, (y - 1 + self.L) % self.L)
                    self.nbr[i_site, 2] = self.xy2i((x + 1) % self.L, y)
                    self.nbr[i_site, 3] = self.xy2i(x, (y + 1) % self.L)
                # Case 2: Open boundary conditions (OBC):
                else:
                    self.N_nbr[i_site] = 0
                    if x > 0:
                        self.nbr[i_site, self.N_nbr[i_site]] = self.xy2i((x - 1 + self.L) % self.L, y)
                        self.N_nbr[i_site] += 1
                    if y > 0:
                        self.nbr[i_site, self.N_nbr[i_site]] = self.xy2i(x, (y - 1 + self.L) % self.L)
                        self.N_nbr[i_site] += 1
                    if x < self.L - 1:
                        self.nbr[i_site, self.N_nbr[i_site]] = self.xy2i((x + 1) % self.L, y)
                        self.N_nbr[i_site] += 1
                    if y < self.L - 1:
                        self.nbr[i_site, self.N_nbr[i_site]] = self.xy2i(x, (y + 1) % self.L)
                        self.N_nbr[i_site] += 1