Flux limiting in the M1 scheme

[tomidakn]

I am now visiting ENS de Lyon and having discussion with RAMSES people.

In this paper (Section 2.3), they point out that the interpolated flux can violate the physical limitation and should be limited to satisfy that.
https://ui.adsabs.harvard.edu/abs/2025arXiv250919447R/abstract
Apparently, this can happen in the current implementation of CR. Do you have any idea? > @yanfeij @changgoo @larmillo

[yanfeij]

Do you mean the limit in section 2.2?

…

On Mon, Mar 2, 2026 at 11:11 AM Kengo TOMIDA ***@***.***> wrote: I am now visiting ENS de Lyon and having discussion with RAMSES people. In this paper (Section 2.3), they point out that the interpolated flux can violate the physical limitation and should be limited to satisfy that. https://ui.adsabs.harvard.edu/abs/2025arXiv250919447R/abstract <https://urldefense.com/v3/__https://ui.adsabs.harvard.edu/abs/2025arXiv250919447R/abstract__;!!DSb-azq1wVFtOg!TjF65NYP0Lg0MSCi63JoITZgcfj3_vt1dYGAr_VLmRA40RQvHAho2PAgf1JeaCr6HaG1vn0EPZUyLyYwgMm-HBta45CMC6Q$> Apparently, this can happen in the current implementation of CR. Do you have any idea? > @yanfeij <https://urldefense.com/v3/__https://github.com/yanfeij__;!!DSb-azq1wVFtOg!TjF65NYP0Lg0MSCi63JoITZgcfj3_vt1dYGAr_VLmRA40RQvHAho2PAgf1JeaCr6HaG1vn0EPZUyLyYwgMm-HBta6Cc57ko$> @changgoo <https://urldefense.com/v3/__https://github.com/changgoo__;!!DSb-azq1wVFtOg!TjF65NYP0Lg0MSCi63JoITZgcfj3_vt1dYGAr_VLmRA40RQvHAho2PAgf1JeaCr6HaG1vn0EPZUyLyYwgMm-HBta7LKIoN4$> @larmillo <https://urldefense.com/v3/__https://github.com/larmillo__;!!DSb-azq1wVFtOg!TjF65NYP0Lg0MSCi63JoITZgcfj3_vt1dYGAr_VLmRA40RQvHAho2PAgf1JeaCr6HaG1vn0EPZUyLyYwgMm-HBta7FIKypw$> — Reply to this email directly, view it on GitHub <https://urldefense.com/v3/__https://github.com/PrincetonUniversity/athena/discussions/715__;!!DSb-azq1wVFtOg!TjF65NYP0Lg0MSCi63JoITZgcfj3_vt1dYGAr_VLmRA40RQvHAho2PAgf1JeaCr6HaG1vn0EPZUyLyYwgMm-HBta7ZnkgJE$>, or unsubscribe <https://urldefense.com/v3/__https://github.com/notifications/unsubscribe-auth/ACCWEJ6LQKPQ7YUQHTWNKOL4OWXCXAVCNFSM6AAAAACWEM3G6WVHI2DSMVQWIX3LMV43ERDJONRXK43TNFXW4OZZGU3DANJZGE__;!!DSb-azq1wVFtOg!TjF65NYP0Lg0MSCi63JoITZgcfj3_vt1dYGAr_VLmRA40RQvHAho2PAgf1JeaCr6HaG1vn0EPZUyLyYwgMm-HBtaDDh6jfw$> . You are receiving this because you were mentioned.Message ID: ***@***.***>

-- Best, Yan-Fei Jiang Research Scientist, CCA, Flatiron Institute, 162 Fifth Avenue New York, NY 10010

[tomidakn]

I meant Section 2.3 (Note on the interpolation step), but that one can be be relevant as well.

[yanfeij]

oh, yes, it can happen. Lucia may have a better ideal on how frequently it happened.

…

On Mon, Mar 2, 2026 at 11:23 AM Kengo TOMIDA ***@***.***> wrote: I meant Section 2.3 (Note on the interpolation step), but that one can be be relevant as well. — Reply to this email directly, view it on GitHub <https://urldefense.com/v3/__https://github.com/PrincetonUniversity/athena/discussions/715*discussioncomment-15974562__;Iw!!DSb-azq1wVFtOg!WGTghVb3L97ZRJoe0LxMVPnPLaqTaEbABEFfxxUw2LhqmnZ6JXN2aD8xoTlBa2Vr956BbjBfwgAeIBmceQOQmMifglcHqr8$>, or unsubscribe <https://urldefense.com/v3/__https://github.com/notifications/unsubscribe-auth/ACCWEJ3GQIZPICOGQ2IU3PD4OWYPDAVCNFSM6AAAAACWEM3G6WVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTKOJXGQ2TMMQ__;!!DSb-azq1wVFtOg!WGTghVb3L97ZRJoe0LxMVPnPLaqTaEbABEFfxxUw2LhqmnZ6JXN2aD8xoTlBa2Vr956BbjBfwgAeIBmceQOQmMift3GvGeo$> . You are receiving this because you were mentioned.Message ID: ***@***.*** com>

-- Best, Yan-Fei Jiang Research Scientist, CCA, Flatiron Institute, 162 Fifth Avenue New York, NY 10010

[larmillo]

I have never checked whether the interpolated flux at the interfaces is smaller than vmax * ec. However, I can say that, on average in the simulation, Fc/(4/3ec) << vmax.

[changgoo]

I just added a trap to check this and restarted from a fully developed CRMHD simulation. I see no cell triggering this trap. So, as Lucia said, in our applications, we haven't seen this. Maybe it can happen in some idealized tests with anomalous sigma.

[tomidakn]

OK, thanks.
When I tried the CR module for my student project on star formation, it crashed at some point. So I think it could be relevant but I need to rerun it to check it.
Let's keep it in mind for the future.