Fix elastic collision

[sosiristseng]

fix #675

I also renewed the facing logic to:

!(dot(r2, v1) > 0 && dot(r1, v2) > 0) && return false

[sosiristseng]

However, some disks would pass each other. Is there any tip so I can fix that?

socialdist2.mp4

[sosiristseng]

The current facing logic does not consider the lower one.

[sosiristseng]

The new logic using dv looks better but fails to pass one collision test.

socialdist2.mp4

[sosiristseng]

I'm reading these lines in tests.

Agents.jl/test/continuous_space_tests.jl

Lines 324 to 330 in 8312904

	# x, which is the changed velocities
	# should be at least the amount of collisions happened divided by 2
	# because half the agents are unmovable (in a collision at most one agent
	# must change velocity)
	@test x > 0
	@test model.c > 0
	@test x ≥ model.c/2

In the tests, only 50 out of 100 agents are movable, so x is at most 50. However, they can collide many times in the simulation (167 times in my case). Should we change the test case @test x ≥ model.c/2?

[Datseris]

Thanks so much, this is a great fix!

Yes please, go ahead and correct the test.

[Datseris]

Ummm @sosiristseng are you perhaps using an automated linter? Can you please revert the linter induced changes? We do not use a linter yet in Agents.jl, but will in the future. Until then, it is best to not include linting changes in pull requests.

[sosiristseng]

I left my formatter on. Will fix that, too.

Edit: It's done. Please have a look.

[codecov-commenter]

Codecov Report

Merging #676 (46b9155) into main (8312904) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #676   +/-   ##
=======================================
  Coverage   90.42%   90.42%           
=======================================
  Files          27       27           
  Lines        1733     1733           
=======================================
  Hits         1567     1567           
  Misses        166      166           

Impacted Files	Coverage Δ
src/spaces/continuous.jl	92.89% <100.00%> (ø)

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[Datseris]

Thank you very much, we appreciate the fix!

[sosiristseng]

Hello, since this is a correctness fix, would you deploy a patch version (like 5.4.4) containing this PR? Or would you like this PR to go into a bigger new version (like 5.5.0) with other PRs?

[Datseris]

I will release 5.5 soon with this in. Can't promise when though! At the moment the main branch is already too far away from 5.4 to publish a patch release. The mean time, feel free to use the development version!