The index i (ii) indicates the mode of transportation, and j indicates the transportation path.

0, 1 variable x(i, j) 1 If i is selected on j, otherwise it is 0; Y(i, ii) 1 If ii is the mode of transportation next to I, otherwise it is 0.

Mathematical model: min z = 20 (sum (c (I, j) * x (I, j))+sum (cc (I, ii) * y (I, ii)).

s.t. sum(i，x(i，j))= 1；

sum(ii，y(i，ii))& lt； = 1;

x(i，j) + x(ii，j+ 1)- 1 & lt； = y(i，ii)；

y(i，ii)& lt； = sum(j，x(i，j))；

X and y are 0, 1 variables.

Results: All of them were transported by rail, and the total transportation cost was 3 100.

Note: Sum operation