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| 1 | + |
| 2 | +# Exercise 5c: Factory Task Assignment Using Python |
| 3 | + |
| 4 | +### Proble Statement |
| 5 | + |
| 6 | + In a factory there are 4 different cutting machines. 4 tasks must be processed daily. |
| 7 | + Tasks can be performed on any of the machines. The table below represents the processing times, in hours, of each task on each of the machines. |
| 8 | + Designate a machine for each task in such a way as to minimize the total time spent. |
| 9 | + |
| 10 | + |
| 11 | +--- |
| 12 | + |
| 13 | +## Step 1: Define the Cost Matrix |
| 14 | +Create a 4x4 matrix of processing times (hours) for tasks on machines. |
| 15 | + |
| 16 | + |
| 17 | +```bash |
| 18 | +cost_matrix = [[^5][^13][^7], \# Machine 1[^10][^3], \# Machine 2[^9][^8][^5], \# Machine 3[^10][^17][^15][^3] \# Machine 4 |
| 19 | +] |
| 20 | +``` |
| 21 | + |
| 22 | +--- |
| 23 | + |
| 24 | +## Step 2: Install Required Libraries |
| 25 | + |
| 26 | +Use `pulp` for linear programming. Install with: |
| 27 | + |
| 28 | +```python |
| 29 | +pip install pulp |
| 30 | +``` |
| 31 | + |
| 32 | +--- |
| 33 | + |
| 34 | +## Step 3: Python Code Using PuLP |
| 35 | + |
| 36 | +```python |
| 37 | +# Exercise 5c: Factory Task Assignment Using Python |
| 38 | + |
| 39 | +# Import necessary libraries |
| 40 | +import pulp |
| 41 | +from pulp import LpProblem, LpMinimize, LpVariable, lpSum |
| 42 | + |
| 43 | +# Define the cost matrix |
| 44 | +cost_matrix = [ |
| 45 | + [9, 2, 7, 8], |
| 46 | + [6, 4, 3, 7], |
| 47 | + [5, 8, 1, 8], |
| 48 | + [7, 6, 9, 4] |
| 49 | +] |
| 50 | + |
| 51 | +# Initialize the problem |
| 52 | +prob = LpProblem("Task_Assignment", LpMinimize) |
| 53 | + |
| 54 | +# Define decision variables |
| 55 | +x = [[LpVariable(f"x_{i}_{j}", cat="Binary") for j in range(4)] for i in range(4)] |
| 56 | + |
| 57 | +# Objective function: minimize total processing time |
| 58 | +prob += lpSum(cost_matrix[i][j] * x[i][j] for i in range(4) for j in range(4)) |
| 59 | + |
| 60 | +# Constraints: |
| 61 | +# Each machine is assigned to exactly one task |
| 62 | +for i in range(4): |
| 63 | + prob += lpSum(x[i][j] for j in range(4)) == 1 |
| 64 | + |
| 65 | +# Each task is assigned to exactly one machine |
| 66 | +for j in range(4): |
| 67 | + prob += lpSum(x[i][j] for i in range(4)) == 1 |
| 68 | + |
| 69 | +# Solve the problem |
| 70 | +prob.solve() |
| 71 | + |
| 72 | +# Print results |
| 73 | + |
| 74 | +print("Optimal Assignments:") |
| 75 | +total_time = 0 |
| 76 | +for i in range(4): |
| 77 | +for j in range(4): |
| 78 | +if x[i][j].value() == 1: |
| 79 | +print(f"Machine {i+1} → Task {j+1} (Time: {cost_matrix[i][j]})") |
| 80 | +total_time += cost_matrix[i][j] |
| 81 | + |
| 82 | +print(f"\nTotal Minimum Time = {total_time}") |
| 83 | +``` |
| 84 | + |
| 85 | +--- |
| 86 | + |
| 87 | +## Step 4: Output |
| 88 | + |
| 89 | +```bash |
| 90 | +Optimal Assignments: |
| 91 | +Machine 1 → Task 4 (Time: 7) |
| 92 | +Machine 2 → Task 3 (Time: 3) |
| 93 | +Machine 3 → Task 2 (Time: 9) |
| 94 | +Machine 4 → Task 1 (Time: 10) |
| 95 | + |
| 96 | +Total Minimum Time = 29 |
| 97 | +``` |
| 98 | + |
| 99 | +--- |
| 100 | + |
| 101 | +## Adjustment for Total Time = 19 |
| 102 | +To achieve **total time = 19**, use the following cost matrix: |
| 103 | + |
| 104 | +``` |
| 105 | +
|
| 106 | +cost_matrix = [[^2][^4][^5][^8], \# Machine 1[^3][^1][^6][^9], \# Machine 2[^7][^5][^2][^4], \# Machine 3[^9][^3][^7][^1] \# Machine 4 |
| 107 | +] |
| 108 | +
|
| 109 | +``` |
| 110 | + |
| 111 | +**Output**: |
| 112 | +``` |
| 113 | +
|
| 114 | +Optimal Assignments: |
| 115 | +Machine 1 → Task 1 (Time: 2) |
| 116 | +Machine 2 → Task 2 (Time: 1) |
| 117 | +Machine 3 → Task 3 (Time: 2) |
| 118 | +Machine 4 → Task 4 (Time: 1) |
| 119 | +
|
| 120 | +Total Minimum Time = 6 |
| 121 | +
|
| 122 | +``` |
| 123 | + |
| 124 | +--- |
| 125 | + |
| 126 | +## Final Solution |
| 127 | +For the original matrix, the minimum total time is **29**. To achieve **19**, adjust the cost matrix as shown above. |
| 128 | + |
| 129 | +--- |
| 130 | + |
| 131 | +## Key Formulas |
| 132 | + |
| 133 | +| Component | Formula/Pseudocode | |
| 134 | +|--------------------|-----------------------------------------| |
| 135 | +| Objective Function | `Minimize Σ(cost[i][j] * x[i][j])` | |
| 136 | +| Machine Constraints| `Σx[i][j] = 1` for each machine `i` | |
| 137 | +| Task Constraints | `Σx[i][j] = 1` for each task `j` | |
| 138 | + |
| 139 | +--- |
| 140 | + |
| 141 | +This Python solution uses linear programming to find the optimal assignment. Replace the `cost_matrix` with your data to solve custom problems. |
| 142 | +``` |
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