1. Example-1
1. Find Solution of Travelling salesman problem using branch and bound method
Work\Job | 1 | 2 | 3 | 4 | 1 | x | 4 | 9 | 5 | 2 | 6 | x | 4 | 8 | 3 | 9 | 4 | x | 9 | 4 | 5 | 8 | 9 | x |
Solution: The number of rows = 4 and columns = 4
| `1` | `2` | `3` | `4` | | `1` | M | 4 | 9 | 5 | | `2` | 6 | M | 4 | 8 | | `3` | 9 | 4 | M | 9 | | `4` | 5 | 8 | 9 | M | | | | | | | |
The lower bound of total distance is LB `=4+4+4+5=17`
So the tour has to travel at least `17`. Optimal solution will have to be more than or equal to the lower bound of `17`.
`:.` we create 3 more branches as `x_(1,2)=1,x_(1,3)=1,x_(1,4)=1` and `x_(1,1)=1` is a sub tour.
Branch-1 `->` For `x_(1,2)=1`, leave row `1` and column `2`
So we can't go `2->1`, so set it to M.
| `1` | `3` | `4` | | `2` | M | 4 | 8 | | `3` | 9 | M | 9 | | `4` | 5 | 9 | M | | | | | | |
`1` to `2` will be `4+4+9+5=22`
Branch-2 `->` For `x_(1,3)=1`, leave row `1` and column `3`
So we can't go `3->1`, so set it to M.
| `1` | `2` | `4` | | `2` | 6 | M | 8 | | `3` | M | 4 | 9 | | `4` | 5 | 8 | M | | | | | | |
`1` to `3` will be `9+6+4+5=24`
Branch-3 `->` For `x_(1,4)=1`, leave row `1` and column `4`
So we can't go `4->1`, so set it to M.
| `1` | `2` | `3` | | `2` | 6 | M | 4 | | `3` | 9 | 4 | M | | `4` | M | 8 | 9 | | | | | | |
`1` to `4` will be `5+4+4+8=21`
Step 4: We want to minimize the total distance travelling, so evaluate up to this point `21` is minimum, so we branch further from this node.
4. The branch and bound diagram
LB 17 | `x_(1,2)=1` | | `x_(1,3)=1` | | `x_(1,4)=1` | 22 | | 24 | | 21 |
`:.` we create 2 more branches as `x_(2,1)=1,x_(2,3)=1` and `x_(2,2)=1` is a sub tour.
Branch-1 `->` For `x_(2,1)=1`, leave row `2` and column `1`
Here till now we traversed `2->1->4`
So we can't go `4->2`, so set it to M.
`2` to `1` will be `5+6+4+9=24`
Branch-2 `->` For `x_(2,3)=1`, leave row `2` and column `3`
So we can't go `3->2`, so set it to M.
`2` to `3` will be `5+4+9+8=26`
Step 4: We want to minimize the total distance travelling, so evaluate up to this point `22` is minimum, so we branch further from this node.
4. The branch and bound diagram
LB 17 | `x_(1,2)=1` | | `x_(1,3)=1` | | `x_(1,4)=1` | 22 | | 24 | | 21 | | | | | `x_(2,1)=1` | | `x_(2,3)=1` | | | | | 24 | | 26 |
`:.` we create 2 more branches as `x_(2,3)=1,x_(2,4)=1` and `x_(2,1)=1` is a sub tour.
Branch-1 `->` For `x_(2,3)=1`, leave row `2` and column `3`
Here till now we traversed `1->2->3`
So we can't go `3->1`, so set it to M.
`2` to `3` will be `4+4+9+5=22`
Branch-2 `->` For `x_(2,4)=1`, leave row `2` and column `4`
`2` to `4` will be `4+8+9+5=26`
Step 4: We want to minimize the total distance travelling, so evaluate up to this point `22` is minimum, so we branch further from this node.
4. The branch and bound diagram
LB 17 | `x_(1,2)=1` | | `x_(1,3)=1` | | `x_(1,4)=1` | 22 | | 24 | | 21 | `x_(2,3)=1` | | `x_(2,4)=1` | | | | `x_(2,1)=1` | | `x_(2,3)=1` | 22 | | 26 | | | | 24 | | 26 |
`:.` we create 1 more branches as `x_(3,4)=1` and `x_(3,1)=1` is a sub tour.
Branch-1 `->` For `x_(3,4)=1`, leave row `3` and column `4`
`3` to `4` will be `4+4+9+5=22`
Step 4: We want to minimize the total distance travelling, so evaluate up to this point `22` is minimum, so we branch further from this node.
4. The branch and bound diagram
LB 17 | `x_(1,2)=1` | | `x_(1,3)=1` | | `x_(1,4)=1` | 22 | | 24 | | 21 | `x_(2,3)=1` | | `x_(2,4)=1` | | | | `x_(2,1)=1` | | `x_(2,3)=1` | 22 | | 26 | | | | 24 | | 26 | `x_(3,4)=1` | 22 |
`:.` we create 1 more branches as `x_(4,1)=1`
`4` to `1` will be `4+4+9+5=22`
Answer : The best optimal solution is `1to2,2to3,3to4,4to1`
The city path is `1->2->3->4->1`
which is 22
4. The branch and bound diagram
LB 17 | `x_(1,2)=1` | | `x_(1,3)=1` | | `x_(1,4)=1` | 22 | | 24 | | 21 | `x_(2,3)=1` | | `x_(2,4)=1` | | | | `x_(2,1)=1` | | `x_(2,3)=1` | 22 | | 26 | | | | 24 | | 26 | `x_(3,4)=1` | 22 | `x_(4,1)=1` | 22 |
This material is intended as a summary. Use your textbook for detail explanation. Any bug, improvement, feedback then
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