888 research outputs found
EECBS: A Bounded-Suboptimal Search for Multi-Agent Path Finding
Multi-Agent Path Finding (MAPF), i.e., finding collision-free paths for
multiple robots, is important for many applications where small runtimes are
necessary, including the kind of automated warehouses operated by Amazon. CBS
is a leading two-level search algorithm for solving MAPF optimally. ECBS is a
bounded-suboptimal variant of CBS that uses focal search to speed up CBS by
sacrificing optimality and instead guaranteeing that the costs of its solutions
are within a given factor of optimal. In this paper, we study how to decrease
its runtime even further using inadmissible heuristics. Motivated by Explicit
Estimation Search (EES), we propose Explicit Estimation CBS (EECBS), a new
bounded-suboptimal variant of CBS, that uses online learning to obtain
inadmissible estimates of the cost of the solution of each high-level node and
uses EES to choose which high-level node to expand next. We also investigate
recent improvements of CBS and adapt them to EECBS. We find that EECBS with the
improvements runs significantly faster than the state-of-the-art
bounded-suboptimal MAPF algorithms ECBS, BCP-7, and eMDD-SAT on a variety of
MAPF instances. We hope that the scalability of EECBS enables additional
applications for bounded-suboptimal MAPF algorithms.Comment: Published at AAAI 202
Learning to Resolve Conflicts for Multi-Agent Path Finding with Conflict-Based Search
Conflict-Based Search (CBS) is a state-of-the-art algorithm for multi-agent
path finding. At the high level, CBS repeatedly detects conflicts and resolves
one of them by splitting the current problem into two subproblems. Previous
work chooses the conflict to resolve by categorizing the conflict into three
classes and always picking a conflict from the highest-priority class. In this
work, we propose an oracle for conflict selection that results in smaller
search tree sizes than the one used in previous work. However, the computation
of the oracle is slow. Thus, we propose a machine-learning framework for
conflict selection that observes the decisions made by the oracle and learns a
conflict-selection strategy represented by a linear ranking function that
imitates the oracle's decisions accurately and quickly. Experiments on
benchmark maps indicate that our method significantly improves the success
rates, the search tree sizes and runtimes over the current state-of-the-art CBS
solver
Incremental Phi*: Incremental Any-Angle Path Planning on Grids
We study path planning on grids with blocked and unblocked cells. Any-angle path-planning algorithms find short paths fast because they propagate information along grid edges without constraining the resulting paths to grid edges. Incremental path-planning algorithms solve a series of similar path-planning problems faster than repeated single-shot searches because they reuse information from the previous search to speed up the next one. In this paper, we combine these ideas by making the any-angle path-planning algorithm Basic Theta* incremental. This is non-trivial because Basic Theta* does not fit the standard assumption that the parent of a vertex in the search tree must also be its neighbor. We present Incremental Phi* and show experimentally that it can speed up Basic Theta* by about one order of magnitude for path planning with the freespace assumption
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