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Minimum Spanning Tree

Minimum Spanning Tree. Spanning tress for Weighted graphs. Minimum Spanning Trees. The Minimum Spanning Tree for a given graph is the Spanning Tree of minimum cost for that graph. Complete Graph. Minimum Spanning Tree. 7. 2. 2. 5. 3. 3. 4. 1. 1.

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Minimum Spanning Tree

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  1. Minimum Spanning Tree Spanning tress for Weighted graphs

  2. Minimum Spanning Trees The Minimum Spanning Tree for a given graph is the Spanning Tree of minimum cost for that graph. Complete Graph Minimum Spanning Tree 7 2 2 5 3 3 4 1 1

  3. Algorithms for Obtaining the Minimum Spanning Tree • Kruskal's Algorithm • Prim's Algorithm

  4. Kruskal's Algorithm This algorithm creates a forest of trees. Initially the forest consists of n single node trees (and no edges). At each step, we add one edge (the cheapest one) so that it joins two trees together. If it were to form a cycle, it would simply link two nodes that were already part of a single connected tree, so that this edge would not be needed.

  5. The steps are: 1. The forest is constructed - with each node in a separate tree. 2. The edges are placed in a priority queue. 3. Until we've added n-1 edges, 1. Extract the cheapest edge from the queue, 2. If it forms a cycle, reject it, 3. Else add it to the forest. Adding it to the forest will join two trees together. Every step will have joined two trees in the forest together, so that at the end, there will only be one tree in T.

  6. Complete Graph 4 B C 4 2 1 A 4 E F 1 2 D 3 10 5 G 5 6 3 4 I H 3 2 J

  7. 4 1 A B A D 4 4 B C B D 4 10 2 B C B J C E 4 2 1 1 5 C F D H A 4 E F 1 6 2 2 D J E G D 3 10 5 G 3 5 F G F I 5 6 3 4 3 4 I G I G J H 3 2 J 2 3 H J I J

  8. Sort Edges (in reality they are placed in a priority queue - not sorted - but sorting them makes the algorithm easier to visualize) 1 1 A D C F 2 2 C E E G 4 2 3 B C H J F G 4 2 1 3 3 G I I J A 4 E F 1 4 4 2 A B B D D 3 10 5 G 4 4 B C G J 5 6 3 4 5 5 I F I D H H 3 2 J 6 10 D J B J

  9. Add Edge 1 1 A D C F 2 2 C E E G 4 2 3 B C H J F G 4 2 1 3 3 G I I J A 4 E F 1 4 4 2 A B B D D 3 10 5 G 4 4 B C G J 5 6 3 4 5 5 I F I D H H 3 2 J 6 10 D J B J

  10. Add Edge 1 1 A D C F 2 2 C E E G 4 2 3 B C H J F G 4 2 1 3 3 G I I J A 4 E F 1 4 4 2 A B B D D 3 10 5 G 4 4 B C G J 5 6 3 4 5 5 I F I D H H 3 2 J 6 10 D J B J

  11. Add Edge 1 1 A D C F 2 2 C E E G 4 2 3 B C H J F G 4 2 1 3 3 G I I J A 4 E F 1 4 4 2 A B B D D 3 10 5 G 4 4 B C G J 5 6 3 4 5 5 I F I D H H 3 2 J 6 10 D J B J

  12. Add Edge 1 1 A D C F 2 2 C E E G 4 2 3 B C H J F G 4 2 1 3 3 G I I J A 4 E F 1 4 4 2 A B B D D 3 10 5 G 4 4 B C G J 5 6 3 4 5 5 I F I D H H 3 2 J 6 10 D J B J

  13. Add Edge 1 1 A D C F 2 2 C E E G 4 2 3 B C H J F G 4 2 1 3 3 G I I J A 4 E F 1 4 4 2 A B B D D 3 10 5 G 4 4 B C G J 5 6 3 4 5 5 I F I D H H 3 2 J 6 10 D J B J

  14. Cycle Don’t Add Edge 1 1 A D C F 2 2 C E E G 4 2 3 B C H J F G 4 2 1 3 3 G I I J A 4 E F 1 4 4 2 A B B D D 3 10 5 G 4 4 B C G J 5 6 3 4 5 5 I F I D H H 3 2 J 6 10 D J B J

  15. Add Edge 1 1 A D C F 2 2 C E E G 4 2 3 B C H J F G 4 2 1 3 3 G I I J A 4 E F 1 4 4 2 A B B D D 3 10 5 G 4 4 B C G J 5 6 3 4 5 5 I F I D H H 3 2 J 6 10 D J B J

  16. Add Edge 1 1 A D C F 2 2 C E E G 4 2 3 B C H J F G 4 2 1 3 3 G I I J A 4 E F 1 4 4 2 A B B D D 3 10 5 G 4 4 B C G J 5 6 3 4 5 5 I F I D H H 3 2 J 6 10 D J B J

  17. Add Edge 1 1 A D C F 2 2 C E E G 4 2 3 B C H J F G 4 2 1 3 3 G I I J A 4 E F 1 4 4 2 A B B D D 3 10 5 G 4 4 B C G J 5 6 3 4 5 5 I F I D H H 3 2 J 6 10 D J B J

  18. Cycle Don’t Add Edge 1 1 A D C F 2 2 C E E G 4 2 3 B C H J F G 4 2 1 3 3 G I I J A 4 E F 1 4 4 2 A B B D D 3 10 5 G 4 4 B C G J 5 6 3 4 5 5 I F I D H H 3 2 J 6 10 D J B J

  19. Add Edge 1 1 A D C F 2 2 C E E G 4 2 3 B C H J F G 4 2 1 3 3 G I I J A 4 E F 1 4 4 2 A B B D D 3 10 5 G 4 4 B C G J 5 6 3 4 5 5 I F I D H H 3 2 J 6 10 D J B J

  20. Minimum Spanning Tree Complete Graph 4 B C 4 B C 4 4 2 1 2 1 A E A 4 F E 1 F 1 2 D 2 D 3 10 G 5 G 3 5 6 3 4 I I H H 3 2 3 J 2 J

  21. Examples

  22. Solutuon

  23. Solution

  24. Underlying graph

  25. Solution(MST)

  26. Prim's Algorithm This algorithm starts with one node. It then, one by one, adds a node that is unconnected to the new graph to the new graph, each time selecting the node whose connecting edge has the smallest weight out of the available nodes’ connecting edges.

  27. The steps are: 1. The new graph is constructed - with one node from the old graph. 2. While new graph has fewer than n nodes, 1. Find the node from the old graph with the smallest connecting edge to the new graph, 2. Add it to the new graph Every step will have joined one node, so that at the end we will have one graph with all the nodes and it will be a minimum spanning tree of the original graph.

  28. Complete Graph 4 B C 4 2 1 A 4 E F 1 2 D 3 10 5 G 5 6 3 4 I H 3 2 J

  29. Old Graph New Graph 4 B C 4 4 B C 2 1 4 2 1 A 4 E F 1 A 4 E F 1 2 D 3 2 10 D 3 5 G 10 5 G 5 6 3 5 6 3 4 I 4 H I H 3 2 J 3 2 J

  30. Old Graph New Graph 4 B C 4 4 B C 2 1 4 2 1 A 4 E F 1 A 4 E F 1 2 D 3 2 10 D 3 5 G 10 5 G 5 6 3 5 6 3 4 I 4 H I H 3 2 J 3 2 J

  31. Old Graph New Graph 4 B C 4 4 B C 2 1 4 2 1 A 4 E F 1 A 4 E F 1 2 D 3 2 10 D 3 5 G 10 5 G 5 6 3 5 6 3 4 I 4 H I H 3 2 J 3 2 J

  32. Old Graph New Graph 4 B C 4 4 B C 2 1 4 2 1 A 4 E F 1 A 4 E F 1 2 D 3 2 10 D 3 5 G 10 5 G 5 6 3 5 6 3 4 I 4 H I H 3 2 J 3 2 J

  33. Old Graph New Graph 4 B C 4 4 B C 2 1 4 2 1 A 4 E F 1 A 4 E F 1 2 D 3 2 10 D 3 5 G 10 5 G 5 6 3 5 6 3 4 I 4 H I H 3 2 J 3 2 J

  34. Old Graph New Graph 4 B C 4 4 B C 2 1 4 2 1 A 4 E F 1 A 4 E F 1 2 D 3 2 10 D 3 5 G 10 5 G 5 6 3 5 6 3 4 I 4 H I H 3 2 J 3 2 J

  35. Old Graph New Graph 4 B C 4 4 B C 2 1 4 2 1 A 4 E F 1 A 4 E F 1 2 D 3 2 10 D 3 5 G 10 5 G 5 6 3 5 6 3 4 I 4 H I H 3 2 J 3 2 J

  36. Old Graph New Graph 4 B C 4 4 B C 2 1 4 2 1 A 4 E F 1 A 4 E F 1 2 D 3 2 10 D 3 5 G 10 5 G 5 6 3 5 6 3 4 I 4 H I H 3 2 J 3 2 J

  37. Old Graph New Graph 4 B C 4 4 B C 2 1 4 2 1 A 4 E F 1 A 4 E F 1 2 D 3 2 10 D 3 5 G 10 5 G 5 6 3 5 6 3 4 I 4 H I H 3 2 J 3 2 J

  38. Old Graph New Graph 4 B C 4 4 B C 2 1 4 2 1 A 4 E F 1 A 4 E F 1 2 D 3 2 10 D 3 5 G 10 5 G 5 6 3 5 6 3 4 I 4 H I H 3 2 J 3 2 J

  39. Complete Graph Minimum Spanning Tree 4 B C 4 4 B C 2 1 4 2 1 A 4 E F 1 A E F 1 2 D 3 2 10 D 5 G G 5 6 3 3 4 I H I H 3 2 J 3 2 J

  40. Example1

  41. Solution

  42. Example2

  43. Solution

  44. Example3

  45. Solution

  46. References Text books 1. Discrete mathematical structures with applications to computer science J.P.Trembly, R.Manohar, Tata M c Graw Hill. 2. Narsingh Deo, ―Graph Theory: With Application to Engineering and Computer Science‖, Prentice Hall of India, 2003. 3. Discrete Mathematical Structures Theory and applications, Mallik and Sen, Cengage. 4. Mathematical foundation of Computer Science Dr.D.S.C

  47. Online Learning References • Discrete Mathematics NPTEL Course by Sudharshan IyeangarIIT Ropar. https://www.hackerearth.com/practice/algorithms/graphs/graph-representation/tutorial/ https://www.quora.com/What-are-some-real-life-examples-of-Breadth-and-Depth-First-Search

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