Exam 6: Distribution and Network Models
Define the variables and constraints necessary in the LP formulation of the transshipment problem.
The transshipment problem involves determining the optimal flow of goods from multiple sources to multiple destinations, while also allowing for intermediate transshipment points where goods can be temporarily stored and transferred. In the LP formulation of the transshipment problem, the following variables and constraints are necessary:
Variables:
1. Flow variables: These represent the amount of goods flowing from a source to a destination, or from a transshipment point to another point. These variables are typically denoted as Xij, where i represents the source or transshipment point, and j represents the destination or transshipment point.
Constraints:
1. Supply constraints: These constraints ensure that the total amount of goods leaving each source does not exceed its supply capacity.
2. Demand constraints: These constraints ensure that the total amount of goods arriving at each destination meets its demand requirements.
3. Transshipment constraints: These constraints ensure that the total amount of goods entering a transshipment point equals the total amount leaving the transshipment point, taking into account any storage or transfer capabilities at the transshipment point.
4. Non-negativity constraints: These constraints ensure that the flow variables are non-negative, as goods cannot flow in negative quantities.
By formulating the transshipment problem as an LP with these variables and constraints, it becomes possible to optimize the flow of goods while satisfying the supply, demand, and transshipment requirements.
When a route in a transportation problem is unacceptable, the corresponding variable can be removed from the LP formulation.
True
A computer manufacturing company wants to develop a monthly plan for shipping finished products from three of its manufacturing facilities to three regional warehouses. It is thinking about using a transportation LP formulation to exactly match capacities and requirements. Data on transportation costs (in dollars per unit), capacities, and requirements are given below.
a. How many variables are involved in the LP formulation?
b. How many constraints are there in this problem?
c. What is the constraint corresponding to Plant B?
d. What is the constraint corresponding to Warehouse 3?

The problem formulation is shown below. Use it to answer the questions a - D.
Xij = each combination of plant i and warehouse j
Min 2.41XA1 + 1.63XA2 + 2.09XA3 + 3.18XB1 + 5.62XB2 + 1.74XB3
+ 4.12XC1 + 3.16XC2 + 3.09XC3
st XA1 + XA2 +XA3 = 4,000 (capacities) XA1 + XB1 +XC1 = 8,000 (requirements)XB1 + XB2 + XB3 = 6,000 XA2 + XB2 +XC2 = 2,000
XC1 +XC2 + XC3 = 3,000 XA3 + XB3 +XC3 = 3,000
a. 9 variables
b. 6 constraints
c. XB1 + XB2 + XB3 = 6,000
d. XA3 + XB3 +XC3 = 3,000
Explain what adjustments can be made to the transportation linear program when there are unacceptable routes.
Converting a transportation problem LP from cost minimization to profit maximization requires only changing the objective function; the conversion does not affect the constraints.
Show both the network and the linear programming formulation for this assignment problem.

A beer distributor needs to plan how to make deliveries from its warehouse (Node 1) to a supermarket (Node 7), as shown in the network below. Develop the LP formulation for finding the shortest route from the warehouse to the supermarket.


A professor has been contacted by four not-for-profit agencies that are willing to work with student consulting teams. The agencies need help with such things as budgeting, information systems, coordinating volunteers, and forecasting. Although each of the four student teams could work with any of the agencies, the professor feels that there is a difference in the amount of time it would take each group to solve each problem. The professor's estimate of the time, in days, is given in the table below. Use the computer solution to see which team works with which project.
ASSIGNMENT PROBLEM
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OBJECTIVE: MINIMIZATION
SUMMARY OF UNIT COST OR REVENUE DATA
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OPTIMAL ASSIGNMENTS COST/REVENUE
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Which of the following is not a characteristic of assignment problems?
The network below shows the flows possible between pairs of six locations. Formulate an LP to find the maximal flow possible from Node 1 to Node 6.


The direction of flow in the shortest-route problem is always out of the origin node and into the destination node.
A transshipment problem is a generalization of the transportation problem in which certain nodes are neither supply nodes nor destination nodes.
The difference between the transportation and assignment problems is that
The assignment problem constraint x31 + x32 + x33 + x34 ≤ 2 means
If a transportation problem has four origins and five destinations, the LP formulation of the problem will have nine constraints.
How is the assignment linear program different from the transportation model?
The assignment problem is a special case of the transportation problem in which all supply and demand values equal one.
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