|*FORM FIELD ProblemDescription*|ProblemDescription|American Steel, an Ohio-based steel manufacturing company, produces steel at its two steel mills located at Youngstown and Pittsburgh. The company distributes finished steel to its retail customers through the distribution network of regional and field warehouses shown below:
The network represents shipment of finished steel from American Steel's two steel mills located at Youngstown (node 1) and Pittsburgh (node 2) to their field warehouses at Albany, Houston, Tempe, and Gary (nodes 6, 7, 8 and 9) through three regional warehouses located at Cincinnati, Kansas City, and Chicago (nodes 3, 4 and 5). Also, some field warehouses can be directly supplied from the steel mills.
Table 1 presents the minimum and maximum flow amounts of steel that may be shipped between different cities along with the cost per 1000 ton/month of shipping the steel. For example, the shipment from Youngstown to Kansas City is contracted out to a railroad company with a minimal shipping clause of 1000 tons/month. However, the railroad cannot ship more then 5000 tons/month due the shortage of rail cars.
Table 1 Arc Costs and Limits
From node
To node
Cost
Minimum
Maximum
Youngstown
Albany
500
-
1000
Youngstown
Cincinnati
350
-
3000
Youngstown
Kansas City
450
1000
5000
Youngstown
Chicago
375
-
5000
Pittsburgh
Cincinnati
350
-
2000
Pittsburgh
Kansas City
450
2000
3000
Pittsburgh
Chicago
400
-
4000
Pittsburgh
Gary
450
-
2000
Cincinnati
Albany
350
1000
5000
Cincinnati
Houston
550
-
6000
Kansas City
Houston
375
-
4000
Kansas City
Tempe
650
-
4000
Chicago
Tempe
600
-
2000
Chicago
Gary
120
-
4000
The current monthly demand at American Steel's four field warehouses is shown in Table 2.
Table 2 Monthly Demands
Field Warehouses
Monthly Demand
Albany, N.Y.
3000
Houston
7000
Tempe
4000
Gary
6000
The Youngstown and Pittsburgh mills can produce up to 10,000 tons and 15,000 tons of steel per month, respectively. The management wants to know the least cost monthly shipment plan.|