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Questions tagged [a-star-search]

27 questions
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Are there graphs for which A* cannot be admissible?

Wikipedia states that "On infinite graphs with a finite branching factor and edge costs that are bounded away from zero $ (d(x,y)>\varepsilon >0$ for some fixed $\varepsilon$), A* is guaranteed to terminate only if there exists a solution." Does…
iaskdumbstuff
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A* (A-star) path finding in continuous environments with "sticky slower" areas

I have a search problem, finding the shortest path for 3 vehicles to their parking spots, in a continuous environment (inputs are continuous for velocity, turn speed) and the location is continuous, ie. the landscape is a discrete grid but within…
mLstudent33
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Comparing classical tree-search algorithms (BFS,DFS,A*,IDS) - when to use one or the other?

I have a question about classical tree-search algorithms as I will have an exam soon and this is the type of questions they might be asking. Although I know how to compare the complexities, optimality, and completeness, I would like to go a bit…
mariaprsk
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Does an optimal path imply the heuristic is admissible?

If we are given an A$^*$ path search with some heuristic $h$ that yields an optimal path, without knowing that the heuristic is admissible beforehand, would this imply that $h$ is admissible?
Paradox
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1 answer

Difference between cost and the heuristic function in A* search

Looking at the image above, thinking in terms of A* search. I don't fully understand the heuristic function. The cost makes sense, so thinking in terms of a traditional map or navigation scenario. I'd see the heuristic function here as the number…
Ewan Valentine
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1 answer

D* Lite - can edge costs be asymmetric?

I'm trying to modify the original D* Lite algorithm adding a margin constraint wrt to any nearby obstacle to be satisfied for each selected cell in the path. This causes the edge cost function between nodes to be asymmetric: let x and y be 2…
dcfg
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Finding multiple paths through a grid such that every grid square is equally used

Setup Here’s the setup: I have an $N$ x $N$ grid of tiles, and a list of $M$ agents that need to move across the grid. Each agent has its own start tile $S(a)$, end tile $E(a)$, and an exact number of steps $D(a)$ it must make. Each step consists…
Paul Accisano
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2 answers

A* without heuristic more efficient than Dijkstra

I am using the module networkx to operate on graphs made from OpenStreetMap. I wanted to compare the shortest path algorithm to find which one is faster, and I compared Dijkstra and A*. The problem is : A* is most of the time faster than Dijkstra…
sophie
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2 answers

cheap multi agent path planning algorithms

I am trying to make a tower defence game where some critters are trying to make their ways through a 2D grid-like obstacle course. The idea is these critters cannot walk into the obstacles or into each other during their path, and they would like to…
Evan Pu
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Heuristic for searching for solutions on an 8-puzzle variant with non-unique tiles

I'm trying to perform an A* search on a particular N-puzzle variant in which some tiles are identical. More specifically, assuming an $m \times m$ grid, there are m colors with m tiles of each. The puzzle is considered solved when tiles form…
Conor Henry
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Tree Search $A^*$ With an Admissible Heuristic Does Not Necessarily Return an Optimal Solution

I know that the title of this post is wrong, but I got stuck on an example. Consider the graph below, which I obtained from here. To the best of my knowledge, the tree search version of $A^*$ fails to provide the optimal path, even though the…
Bored Comedy
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Why Can Johnson’s Algorithm Handle Negative Weights but A* Cannot?

I'm trying to understand why Johnson’s algorithm can handle graphs with negative edge weights by using a potential function, while A* cannot, even though both use similar weight adjustments. Johnson’s Algorithm: Uses Bellman–Ford to compute exact…
miiky123
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Shortest path between two nodes with time-dependent edge weights

I have city traffic data. The roads are represented as a directed graph (a road can have traffic both ways, at most two-lane roads included), vertices being points on a map where two or more road segments join together. I want to find the shortest…
Sgg8
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Simplified Memory Bounded A*

I have been studying the SMA* algorithm and I am having trouble understanding the backup operation. Specifically, I don't understand why the f value of a child node should be the maximum of its own f value and its parent's f value, as described in…
Error 404
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Optimality of A* algorithm

In the book Artificial Intelligence a Modern Approach 4th edition, the author claims that the A* algorithm is cost-optimal if the heuristic function is admissible (never overestimates the remaining true cost). Additionally, if the heuristic is…
user101998
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