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Transportation and Assignment Models

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The Transportation Problem

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The transportation problem seeks to minimize the cost of distributing a product from several sources to various destinations. Differences: It is a type of linear programming problem; different from general LP due to its structure. Similarities: Uses LP simplex or modified simplex method for solution. Solution approaches: The Northwest Corner Method, The Minimum Cost Method, The Vogel Approximation Method.

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Linear Programming Solution to Transportation Problems

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Linear programming (LP) can be used to solve transportation problems with a more mathematical and optimal approach. Differences: LP solutions are optimal, not heuristic. Similarities: All methods ultimately use LP formulations for optimality. Solution approaches: Formulate the problem as an LP, apply the simplex or modified simplex methods, iterate to find the optimal solution.

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The Hungarian Method for Assignment Problems

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The Hungarian Method finds the optimal solution for assignment problems. Differences: It is a combinatorial optimization algorithm specific to assignment problems. Similarities: Related to other matrix minimization methods in LP. Solution approaches: Subtract row and column minima, cover all zeros with a minimum number of lines, adjust the uncovered numbers, and repeat until an optimal assignment is found.

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The Vogel Approximation Method (VAM)

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VAM is a heuristic used to find a good initial solution to the transportation problem by minimizing penalties. Differences: It considers penalties for not choosing the next best cell. Similarities: Also a method for finding an initial feasible solution. Solution approaches: Calculate penalties, choose the highest penalty cell, allocate as much as possible, adjust remaining supply and demand, repeat until all needs are satisfied.

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The Northwest Corner Method

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The Northwest Corner Method is a heuristic for finding an initial feasible solution to the transportation problem. Differences: It does not guarantee the optimal solution. Solutions are found at the 'northwest corner' of the matrix. Similarities: It's a stepping stone to move towards optimality using other methods. Solution approaches: Selecting the northwest-most cell, allocating as much as possible, and moving south or east in the matrix.

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Balanced vs Unbalanced Transportation Problems

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Balanced transportation problems have total supply equal to total demand, while unbalanced ones need additional dummy rows or columns. Differences: The need for dummy variables to balance the problem. Similarities: Both can be solved using similar methods. Solution approaches: Add dummy rows or columns with zero cost for unbalanced problems, then apply the standard transportation problem-solving methods.

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The Assignment Problem

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The assignment problem deals with finding a one-to-one matching between tasks and agents. Differences: It's a special case of the transportation problem with all supply and demand equal to 1. Similarities: Hungarian Method used is a special form of the dual-simplex method. Solution approaches: Hungarian Method, Linear Programming, Branch and Bound Technique.

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Cycle Method in Transportation Problems

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The cycle method is used in solving transportation problems by identifying cycles within the solution matrix to make adjustments towards optimality. Differences: It is used after an initial solution is found. Similarities: It helps improve upon the current solution, heading towards optimality. Solution approaches: Identify closed loops in the matrix, make adjustments to the allocation of the loop cells, and repeat until no improvements are found.

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Sensitivity Analysis in Transportation and Assignment Problems

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Sensitivity analysis examines the effect of changes in parameters on the optimal solution of transportation and assignment problems. Differences: Focuses on changes and their impacts, not on finding the initial solution. Similarities: Necessary for understanding the robustness of the solution. Solution approaches: Alter parameters like costs, supply, and demand, re-solve the problem and evaluate changes in the optimal solution and cost.

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The Minimum Cost Method

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The Minimum Cost Method is another initial feasible solution heuristic for transportation problems. Differences: Favors cells with the lowest cost, not position-based like Northwest Corner Method. Similarities: It is another starting point for optimization. Solution approaches: Find the minimum cost cell, allocate as much as possible, adjust supply and demand, and repeat until all are filled.

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