Mistake in BlobTest_3D example

[sperneder]

Hi SWIFT team,

I was trying to use the makeIC.py file from the BlobTest_3D example for a different simulation when I noticed a mistake in the function generate_bcc_lattice:

SWIFT/examples/HydroTests/BlobTest_3D/makeIC.py

Lines 35 to 42 in 2287ed5

	def generate_bcc_lattice(num_on_side, side_length=1.0):
	cube = generate_cube(num_on_side // 2, side_length)
	mips = side_length / num_on_side
	positions = np.concatenate([cube, cube + mips * 0.5])
	return positions

The function should create a bcc lattice by generating a grid, and adding a second grid that is shifted by a half step in all 3 directions. However in this case the half step mips = side_length / num_on_side is calculated wrong, which then results in the second grid being moved too little.

A 2D plot for a grid generated with this function (with num_on_side = 10) looks like this:

A possible solution would be to change the line mips = side_length / num_on_side to mips = side_length / (num_on_side // 2).
This would result in a grid that looks like this:

[JBorrow]

Thanks! You're totally correct here. I've looked at some of our private checkouts of the script that we've used for various works, and they have this issue corrected; it must just be something that we've forgotten to push upstream at some point. I will address this in the GitLab version of the repo (our GitHub repo is just a copy of the GitLab one) and close this when appropriate.

Thanks again for reporting this. It's very helpful! Glad you're making use of the script; I would suggest that for now you go ahead and use your fixed version that correctly creates the BCC lattice.

[JBorrow]

The GitLab merge request is here: https://gitlab.cosma.dur.ac.uk/swift/swiftsim/-/merge_requests/1733

[JBorrow]

Thank you! We've now fixed this in the main codebase. The changes will synchronise with the master branch on GitHub tonight.

https://gitlab.cosma.dur.ac.uk/swift/swiftsim/-/merge_requests/1733/diffs#note_49912

Thanks again for reporting this!