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dijkstra A*和D*等算法介绍.pdf

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Robotic Motion Planning: A* and D* Search Robotics Institute 16-735 http://www.cs.cmu.edu/~motionplanning Howie Choset http://www.cs.cmu.edu/~choset 16-735, Howie Choset with slides from Ayorkor Mills-Tettey, Vincent Lee-Shue Jr. Prasad Narendra Atkar, Kevin Tantisevi
Outline • Overview of Search Techniques • A* Search • D* Search • D* Lite 2
Graphs Collection of Edges and Nodes (Vertices) A tree 3
Search in Path Planning • Find a path between two locations in an unknown, partially known, or known environment • Search Performance – Completeness – Optimality → Operating cost – Space Complexity – Time Complexity 4
Search • Uninformed Search – Use no information obtained from the environment – Blind Search: BFS (Wavefront), DFS • Informed Search – Use evaluation function – More efficient – Heuristic Search: A*, D*, etc. 5
Uninformed Search Graph Search from A to N BFS 6
Informed Search: A* Notation • n → node/state • c(n1,n2) → the length of an edge connecting between n1 and n2 • b(n1) = n2 → backpointer of a node n1 to a node n2. 7
Informed Search: A* • Evaluation function, f(n) = g(n) + h(n) • Operating cost function, g(n) – Actual operating cost having been already traversed • Heuristic function, h(n) – Information used to find the promising node to traverse – Admissible → never overestimate the actual path cost Cost on a grid 8
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