Chapter 7: Q6E (page 240)
Give an example of a linear program in two variables whose feasible region is infinite, but such that there is an optimum solution of bounded cost.
Short Answer
Example 1:
Example 2:
Chapter 7: Q6E (page 240)
Give an example of a linear program in two variables whose feasible region is infinite, but such that there is an optimum solution of bounded cost.
Example 1:
Example 2:
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Get started for freeShow that the change-making problem (Exercise) can be formulated as an integer linear program. Can we solve this program as an LP, in the certainty that the solution will turn out to be integral (as in the case of bipartite matching)? Either prove it or give a counterexample.
Consider the following linear program.
maximize 5x+3y
Plot the feasible region and identify the optimal solution.
Hollywood. A film producer is seeking actors and investors for his new movie. There are available actors; actor charges dollars. For funding, there are available investors. Investor will provide dollars, but only on the condition that certain actors are included in the cast (all of these actors must be chosen in order to receive funding from investorrole="math" localid="1658404523817" ).
The producer’s profit is the sum of the payments from investors minus the payments to actors. The goal is to maximize this profit.
(a) Express this problem as an integer linear program in which the variables take on values .
(b) Now relax this to a linear program, and show that there must in fact be an integral optimal solution (as is the case, for example, with maximum flow and bipartite matching).
Question: Duckwheat is produced in Kansas and Mexico and consumed in New York and California. Kansas produces 15 shnupells of duckwheat and Mexico 8. Meanwhile, New York consumes 10 shnupells and California 13. The transportation costs per shnupell are \(4 from Mexico to New York, \)1 from Mexico to California, \(2 from Kansas to New York, and \)3 and from Kansas to California. Write a linear program that decides the amounts of duckwheat (in shnupells and fractions of a shnupell) to be transported from each producer to each consumer, so as to minimize the overall transportation cost
The dual of maximum flow. Consider the following network with edge capacities
(a) Write the problem of finding the maximum flow from as a linear program.
(b) Write down the dual of this linear program. There should be a dual variable for each edge of the network and for each vertex other than
Now we’ll solve the same problem in full generality. Recall the linear program for a general maximum flow problem (Section 7.2).
(c) Write down the dual of this general flow LP, using a variablefor each edge and for each vertex
(d) Show that any solution to the general dual LP must satisfy the following property: for any directed path from in the network, the sum of the values along the path must be at least .
(e) What are the intuitive meanings of the dual variables? Show that anycut in the network can be translated into a dual feasible solution whose cost is exactly the capacity of that cut.
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