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search techniques
ssr(state space representations) concerns machine recognizable representations, and search techniques concerns how to reach goal state.
ssr rules dt ann search fc/bc tree traversal propagation what knowledge how reasoning 1 (classical ai) search techniques search techniques:
a systemic manner to find a sequence of operators that transforms from initial state to goal state.
breadth-first search (bfs), depth-first search (dfs), branch&bound(b&b)
hill-climbing search (hcs), best-first search (bestfs), a* search
2 search techniques 3 problem with search: combinatorial explosion
branching factor (b): number of operators available at a state.
depth (d): distance between initial and desired state (may be very high).
size of search space bd (in 10 step 8-puzzle ~ 210 ~ 410).
example: in 8-puzzle, b is xxx-xxx (chess?)
two approaches to solve combinatorial explosion.
goal decomposition bd ¢¡ n*bd/n heuristic search b¢¥d where b¢¥<< b heuristic search 4 heuristics
useful information or rule of thumbs that guide search through a problem space
may not be totally correct, but in general helpful to reach goal.
example:
never apply an operator that leads to a state that has already been visited.
in navigator, prefer the way to reduce linear distance most to destination.
in 8-puzzle, prefer to move a tile into its desired position (number of tiles in position).
heuristic search
search techniques using heuristic knowledge.
examples:
hill-climbing search (hc), best-first search (bestfs), a* search(a*)
search techniques 5 no extra knowledge bfs: breadth first search dfs: depth first search accumulated cost (g) b&b: branch and bound heuristic estimates (h) bestfs: best first search simple hcs: simple hill climbing search steepest ascent hill climbing search combined evaluation (g h): a*: bestfs using gh¡¯
which one will be best?
answer: under what conditions!
b(5) c(7) d(20) e(4) f(0) 3 5 4 g(0) 10 problem 6
for the following search space, find exploration sequences for various search techniques-bfs, dfs,
b&b, bestfs, simple hcs, steepest-ascent hcs, a*, etc.
a(10) 4 8 knowledge representation knowledge (ÀÌÇÏ »ý·«)
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