Problems with DemoImpactInitCond

[jmtaylor384]

I am trying to set up SWIFT on a Mac (Intel 2018) and have successfully installed up to the point where the SodShock3D example runs correctly. However, I am having a problem with DemoImpactInitCond under Planetary. When I run the example, there are many instances of these warnings within the data:

"hydro_prepare gradient: WARNING: h ~ h_max for particle with ID # hydro_part_has_no_neighbours"
"hydro_part_has_no_neighbours: WARNING: Gas particle with ID # treated as having no neighbours"

This is the main functionality of SWIFT that I use, so any insight on what could be causing this issue would be greatly appreciated. Thank you in advance.

[MatthieuSchaller]

Hi,

This is normally expected. These are just warnings. When particles get ejected from their planets, they get very large smoothing lengths as they can't find ~50 neighbours close-by. The code then issues warnings as there are setups where this is not expected.

[MatthieuSchaller]

@jkeger might have more input

[jkeger]

Hi, please could you paste exactly the configuration and execution commands you're using? Like Matthieu said, it's normal and (potentially) okay for particles to ready h = h_max if they are flying out to low densities. However, I don't see these messages when I run the example, and hydro_prepare_gradient in the planetary hydro scheme is empty, so shouldn't be being called regardless.

In terms of doing your own runs, you can make a choice of h_max based on the minimum density that you need your simulation to be able to resolve. However, setting h_max to be very large can lead to much slower runtimes. If you're concerned that your science results are unusually sensitive to numerical choices like h_max, then I'd recommend running duplicate simulations with e.g. a few different h_max to at least allow to you constrain the magnitude of the effect.