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Best First Search priority queue presents a weird behavior #919

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Best First Search priority queue presents a weird behavior#919
@kecol

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@kecol
kecol
opened on May 1, 2018

Looks like this modification to PriorityQueue.contains() method makes the Best First Search original implementation fails with the frontier management. The queue will not work as expected by BFS algorithm and the frontier will grow in size every time a repeated situation/state is found.

In class PriotityQueue

aima-python/utils.py

Lines 726 to 728 in 5889656

def __contains__(self, item):
"""Return True if item in PriorityQueue."""
return (self.f(item), item) in self.heap

Inside best_first_graph_search method (lines 276 and 278).

aima-python/search.py

Lines 275 to 282 in 5889656

for child in node.expand(problem):
if child.state not in explored and child not in frontier:
frontier.append(child)
elif child in frontier:
incumbent = frontier[child]
if f(child) < f(incumbent):
del frontier[incumbent]
frontier.append(child)

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