Formulating the Assignment Problem as a Linear Programming Problem

Oct 13, 2025 by wbrum.org 1 views

Introduction

The assignment problem is a classic problem in combinatorial optimization and operations research. It involves finding the optimal assignment of tasks or jobs to workers or agents in a way that minimizes the total cost or maximizes the total profit. In this article, we will discuss the assignment problem for minimization and provide a step-by-step solution to a specific example.

What is the Assignment Problem?

The assignment problem is a type of linear programming problem that involves finding the optimal assignment of tasks or jobs to workers or agents. It is a classic problem in combinatorial optimization and operations research. The problem can be formulated as follows:

We have a set of tasks or jobs, denoted by the set J = {1, 2, ..., n}.
We have a set of workers or agents, denoted by the set W = {1, 2, ..., m}.
Each task or job has a cost or profit associated with it, denoted by the matrix C = [c_ij], where c_ij is the cost or profit of assigning task i to worker j.
The objective is to find the optimal assignment of tasks or jobs to workers or agents that minimizes the total cost or maximizes the total profit.

Formulating the Assignment Problem as a Linear Programming Problem

The assignment problem can be formulated as a linear programming problem as follows:

Let x_ij be a binary variable that represents the assignment of task i to worker j. If task i is assigned to worker j, then x_ij = 1, otherwise x_ij = 0.
The objective function is to minimize the total cost or maximize the total profit, which can be written as:

∑∑ c_ij x_ij

The constraints are:

∑ x_ij = 1 for all i in J ∑ x_ij = 1 for all j in W x_ij ∈ {0, 1} for all i in J and j in W

Example: Solving the Assignment Problem for Minimization

Let's consider the following example:

Task	Worker 1	Worker 2	Worker 3	Worker 4	Worker 5	Worker 6
1	18	26	11	13	28	14
2	26	14	26	11	13	28
3	11	13	28	14	26	26

The cost matrix C is given by:

C = [[18, 26, 11, 13, 28, 14], [26, 14, 26, 11, 13, 28], [11, 13, 28, 14, 26, 26]]

The objective is to find the optimal assignment of tasks to workers that minimizes the total cost.

Step 1: Create a Cost Matrix

The cost matrix C is given by:

C = [[18, 26, 11, 13, 28, 14], [26, 14, 26, 11, 13, 28], [11, 13, 28, 14, 26, 26]]

Step 2: Find the Minimum Cost

To find the minimum cost, we need to find the minimum value in each row of the cost matrix C.

Task	Min Cost
1	11
2	11
3	11

Step 3: Find the Optimal Assignment

To find the optimal assignment, we need to find the worker with the minimum cost for each task.

Task	Optimal Worker
1	3
2	3
3	3

Step 4: Calculate the Total Cost

To calculate the total cost, we need to sum up the costs of the optimal assignment.

Total Cost = 11 + 11 + 11 = 33

Conclusion

In this article, we discussed the assignment problem for minimization and provided a step-by-step solution to a specific example. We formulated the assignment problem as a linear programming problem and used the Hungarian algorithm to find the optimal assignment. The optimal assignment was found to be:

Task	Optimal Worker
1	3
2	3
3	3

The total cost of the optimal assignment was found to be 33.

References

Kuhn, H. W. (1955). The Hungarian method for the assignment problem. Naval Research Logistics Quarterly, 2(1-2), 83-97.
Munkres, J. (1957). Algorithms for the assignment and transportation problems. SIAM Journal on Applied Mathematics, 5(1), 32-38.

Introduction

In our previous article, we discussed the assignment problem for minimization and provided a step-by-step solution to a specific example. In this article, we will answer some frequently asked questions (FAQs) related to the assignment problem for minimization.

Q: What is the assignment problem?

A: The assignment problem is a type of linear programming problem that involves finding the optimal assignment of tasks or jobs to workers or agents in a way that minimizes the total cost or maximizes the total profit.

Q: What is the Hungarian algorithm?

A: The Hungarian algorithm is a popular algorithm for solving the assignment problem. It is a simple and efficient algorithm that can be used to solve large-scale assignment problems.

Q: How do I formulate the assignment problem as a linear programming problem?

A: To formulate the assignment problem as a linear programming problem, you need to define the following:

A set of tasks or jobs, denoted by the set J = {1, 2, ..., n}.
A set of workers or agents, denoted by the set W = {1, 2, ..., m}.
A cost or profit matrix C = [c_ij], where c_ij is the cost or profit of assigning task i to worker j.
A binary variable x_ij that represents the assignment of task i to worker j. If task i is assigned to worker j, then x_ij = 1, otherwise x_ij = 0.

Q: How do I find the optimal assignment using the Hungarian algorithm?

A: To find the optimal assignment using the Hungarian algorithm, you need to follow these steps:

Create a cost matrix C.
Find the minimum cost in each row of the cost matrix C.
Find the worker with the minimum cost for each task.
Calculate the total cost of the optimal assignment.

Q: What is the time complexity of the Hungarian algorithm?

A: The time complexity of the Hungarian algorithm is O(n^3), where n is the number of tasks or jobs.

Q: Can the Hungarian algorithm be used to solve other types of linear programming problems?

A: Yes, the Hungarian algorithm can be used to solve other types of linear programming problems, such as the transportation problem and the maximum flow problem.

Q: What are some applications of the assignment problem?

A: The assignment problem has many applications in fields such as logistics, supply chain management, and resource allocation.

Q: How do I implement the Hungarian algorithm in a programming language?

A: The Hungarian algorithm can be implemented in a programming language such as Python or Java. There are many libraries and frameworks available that provide implementations of the Hungarian algorithm.

Conclusion

In this article, we answered some frequently asked questions (FAQs) related to the assignment problem for minimization. We provided a step-by-step solution to a specific example and discussed the Hungarian algorithm, a popular algorithm for solving the assignment problem.

References

Kuhn, H. W. (1955). The Hungarian method for the assignment problem. Naval Research Logistics Quarterly, 2(1-2), 83-97.
Munkres, J. (1957). Algorithms for the assignment and transportation problems. SIAM Journal on Applied Mathematics, 5(1), 32-38.