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# CSE633

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### CSE633

1. 1. Parallel Implementation of Dijkstra’s and Bellman Ford Algorithm Team 26 B ● Priyanka Ramanuja Kulkarni ● Meenakshi Muthuraman ● Aslesha Pansare ● Nikhil Kataria
2. 2. Single Source Shortest Path Problem ● The Problem of finding the shortest path from a source vertex S to all vertices in the graph ● Weighted graph G = (V,E) ● Distance from S to all the vertices
3. 3. Dijkstra’s Algorithm ● Solution to single source shortest path algorithm in graph theory ○ Both directed and undirected graphs ○ All edges must have non- negative weights ○ Graph must be connected ○ Dijkstra’s algorithm runs in
4. 4. Pseudocode of Dijkstra’s Algorithm
5. 5. Negative Cycles A negative cycle is a cycle in a weighted graph whose total weight is negative
6. 6. Bellman Ford’s Algorithm BELLMAN-FORD(G,w,s) 1. INITIALIZE-SINGLE-SOURCE(G,s) 2. for i = 1 to |G.V|-1 3. for each edge (u,v) ∈ G.E 4. RELAX(u,v,w) 5. for each edge (u,v) ∈ G.E 6. if v.d > u.d + w(u,v) 7. return FALSE 8. return TRUE BELLMAN-FORD(G,w,s) 1. INITIALIZE-SINGLE-SOURCE(G,s) 2. for i = 1 to |G.V|-1 3. for each edge (u,v) ∈ G.E 4. RELAX(u,v,w) 5. for each edge (u,v) ∈ G.E 6. if v.d > u.d + w(u,v) 7. return FALSE 8. return TRUE ● Worst case performance - 0 (|V||E|) ● Space Complexity - 0(|V|)
7. 7. Comparing Sequential performance
8. 8. Assumptions ● All the edges are undirected ● We consider a sparse matrix for the initial distance vector ● Each vertex is connected to at least 1 other vertex ● The weights of the edges are assigned randomly with a restriction on the x-axis rand()
9. 9. Parallel Dijkstra’s Algorithm ● On each cluster identify vertices closest to the source vertex ● Use parallel prefix to select the globally closest vertex ● Broadcast the results to all cores ● On each cluster update the distance vectors ● Running time = 0(V2 /P + V*log(P))
10. 10. Parallel Approach 1.Allocate graph nodes to different processors. 2.Shortest distance is computed using parallel prefix. 3. Broadcast the Result to all nodes after finding closest path. ❏ MPI_Reduce(MPI_IN_PLACE,nextAN,1,MPI_INT,MPI_SUM,0,MPI_COMM_WORLD); ❏ MPI_Bcast( G->node[0], G->N*G->N, MPI_CHAR, 0, MPI_COMM_WORLD);
11. 11. Dijkstra’s sequential Vs Parallel Implementation
12. 12. Dijkstra’s: #nodes v/s Running time
13. 13. Djikstra’s: Speed up
14. 14. Dijkstra’s: Cost Analysis
15. 15. Bellman Ford: sequential vs parallel
16. 16. Bellman Ford: Running Time v/s # of Nodes
17. 17. Bellman Ford: Speedup
18. 18. Bellman Ford: Cost Analysis
19. 19. Comparing parallel performance
20. 20. References ● Implementing Parallel Shortest-Paths Algorithms (1994) by by Marios Papaefthymiou and Joseph Rodrigue ● Algorithms Sequential & Parallel: A Unified Approach / Edition 2 by Russ Miller and Lawrence Boxer ● An Experimental Study of a Parallel Shortest Path Algorithm for Solving Large-Scale Graph Instances by Kamesh Madduri and David A. Bader, Georgia Institute of Technology and Jonathan W. Berry Sandia National Laboratories and Joseph R. Crobak, Rutgers University ● Parallel Algorithms by Guy E. Blelloch and Bruce M. Maggs, School of Computer Science, Carnegie Mellon University