By analyzing the diagram 1, we use Floyd algorithm to find the shortest path between railway network and highway network, and then convert it into minimum transportation, remove the attributes of railway and highway, make the transportation network into a price list of supply and demand transportation, and then establish a nonlinear programming model with total cost as the objective function. Using Lingo software, we found that the optimal solution of the problem 1 is1278.632 million yuan.

Through the analysis of the calculation results of lingo in question 1, we come to the conclusion that the change of steel pipe sales price in S5 steel plant has the greatest influence on the mining and transportation plan and total cost, and the change of steel pipe output ceiling in S 1 steel plant has the greatest influence on the mining and transportation plan and total cost.

The modeling principle of question 3 is the same as that of question 1. Using Lingo software, the following optimal solution can be obtained.

1407 1.49 million yuan.