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Clarify ContinuousSpace.get_neighbors behavior with multiple agents at same position#2599

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quaquel merged 7 commits intomesa:mainfrom
quaquel:bugfix_continuous_space
Jan 6, 2025
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Clarify ContinuousSpace.get_neighbors behavior with multiple agents at same position#2599
quaquel merged 7 commits intomesa:mainfrom
quaquel:bugfix_continuous_space

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@quaquel quaquel commented Jan 6, 2025 •
edited by EwoutH
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This PR clarifies the behavior of ContinuousSpace.get_neighbors when multiple agents occupy the same position.

Changes:

  1. Add detailed documentation to get_neighbors explaining how include_center=False affects agents at the same position
  2. Update the Boids example to demonstrate the recommended pattern of using include_center=True and filtering out self

Context:
When multiple agents occupy the same position and include_center=False is used, all agents at that position are excluded from the results - not just the center agent. This is the expected behavior, but was not clearly documented. Rather than making a breaking change to the API, this PR:

  1. Documents the behavior explicitly
  2. Shows the recommended pattern of using include_center=True and filtering unwanted agents

Example usage:

# Before (potentially misses "neighbors" at same position):
neighbors = space.get_neighbors(self.pos, radius, include_center=False)

# Workaround:
neighbors = space.get_neighbors(self.pos, radius, include_center=True)
neighbors = [n for n in neighbors if n is not self]

Closes #2592.

@quaquel quaquel added bug Release notes label docs Release notes label labels Jan 6, 2025
@quaquel quaquel linked an issue Jan 6, 2025 that may be closed by this pull request
bug in ContinuousSpace.get_neighbors #2592
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github-actions bot commented Jan 6, 2025

Performance benchmarks:

Model Size Init time [95% CI] Run time [95% CI]
BoltzmannWealth small 🔵 -0.1% [-2.0%, +1.9%] 🔵 +0.5% [+0.4%, +0.6%]
BoltzmannWealth large 🔵 -0.4% [-0.6%, -0.1%] 🔵 -1.2% [-2.0%, -0.4%]
Schelling small 🔵 +0.2% [-0.2%, +0.5%] 🔵 +0.3% [+0.2%, +0.4%]
Schelling large 🔵 -0.1% [-2.0%, +1.2%] 🔵 +0.6% [-0.2%, +1.6%]
WolfSheep small 🔵 +0.8% [+0.2%, +1.4%] 🔵 +1.8% [-3.6%, +7.1%]
WolfSheep large 🔵 +0.8% [-0.1%, +1.7%] 🔵 +1.5% [+0.5%, +2.4%]
BoidFlockers small 🔵 -1.1% [-1.7%, -0.4%] 🔵 +0.0% [-0.8%, +0.8%]
BoidFlockers large 🔵 -1.6% [-2.4%, -0.8%] 🔵 -0.8% [-1.4%, -0.1%]

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EwoutH commented Jan 6, 2025

Sounds like it’s working like intended, right? All agents with the same location are not considered neighbors.

Specifically for flocking, since agents are on continuous coordinates, isn’t the chance extremely small a neighbor has the exact same location (fp32 precision?) as another agent?

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quaquel commented Jan 6, 2025

Sounds like it’s working like intended, right? All agents with the same location are not considered neighbors.

I beg to differ. To me, if a given agent X asks for its neighbors, I expect to get all neighbors even if there happens to be an agent Y on the exact same location this agent Y is still a neighbor of agent X.

Specifically for flocking, since agents are on continuous coordinates, isn’t the chance extremely small a neighbor has the exact same location (fp32 precision?) as another agent?

Yes, this is very much an edge-case kind of issue, which is why the documentation solution is fine as far as I am concerned.

tpike3
tpike3 reviewed Jan 6, 2025
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EwoutH
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Update mesa/space.py
436a589 
Co-authored-by: Ewout ter Hoeven <[email protected]>
EwoutH
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Looks good, thanks!

@EwoutH EwoutH added example Changes the examples or adds to them. and removed bug Release notes label labels Jan 6, 2025
@quaquel quaquel merged commit 72e8acc into mesa:main Jan 6, 2025
@quaquel quaquel deleted the bugfix_continuous_space branch January 6, 2025 15:24
@EwoutH EwoutH changed the title Basic bugfix for bug ContinuousSpace.get_neighbors Clarify ContinuousSpace.get_neighbors behavior with multiple agents at same position Jan 6, 2025
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EwoutH commented Jan 6, 2025

I updated the PR title and body to reflect the final changes. Feel free to adjust further or let me know if you don't like it.

@EwoutH EwoutH mentioned this pull request Jan 11, 2025
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jackiekazil pushed a commit that referenced this pull request Feb 14, 2025
@quaquel @pre-commit-ci
@EwoutH @jackiekazil
Basic bugfix for bug ContinuousSpace.get_neighbors (#2599)
49b8864 
Co-authored-by: Ewout ter Hoeven <[email protected]>

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Ewout ter Hoeven <[email protected]>
tpike3 pushed a commit to tpike3/mesa that referenced this pull request Mar 25, 2025
@quaquel @pre-commit-ci
@EwoutH @tpike3
Basic bugfix for bug ContinuousSpace.get_neighbors (mesa#2599)
3529b7d 
Co-authored-by: Ewout ter Hoeven <[email protected]>

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Ewout ter Hoeven <[email protected]>
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bug in ContinuousSpace.get_neighbors

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