[yt-users] wired square in enzo DM slice map

[Nathan Goldbaum]

If this is a plot of the Enzo "Dark_Matter_Density" field that gets written
to Enzo output files, then the artifacts you're seeing are generated by
Enzo. yt is just plotting whatever is in your output files.

You should be able to see how Enzo generates this field by grepping the
codebase for "OutputSmoothedDarkMatter" and looking at the relevant code
sections. One key thing: I believe Enzo's CIC deposit machinery doesn't
handle grid boundary conditions properly, so and particles that should
contribute to the cells that are at a grid boundary will only contribute if
they are on one side of the grid boundary. This would lead to the deficits
you're seeing. I haven't looked at that code in a while so please excuse me
if I'm misremembering here.

Hope that's helpful,

Nathan

On Mon, Jun 15, 2015 at 9:59 AM, Junhwan Choi (최준환) <choi.junhwan at gmail.com>
wrote:

> Hi yt users,
>
> I have asked a similar question previously but I did get partial
> answer so that I ask again.
> I have made cosmological IC from MUSIC and run with enzo.
> I made the DM density map with velocity arrow at z=200 which is
> initial redshift using yt (and attach the figure).
> It shows the wired square feature.
> Previously, John wise suggested me to use enzo SPH smoothing to remove
> this issue and it worked.
> But, after test a few more run, I have couple more fundamental
> questions on this issue.
>
> 1) Is this wired square effect is real effect in enzo or visualization in
> yt?
>     If this is an intrinsic enzo effect, we can say that DM gravity
> calculation at high-z some kind of error.
>     If this is an visualization effect, I found that other enzo
> simulation using different IC generator does not show this effect (see
> question 2).
>     This difference makes me very confused.
>
> 2) I tested with other IC generator and I do not see the wired square
> feature.
>     I found that other IC generator output real DM position while
> MUSIC IC generate displacement of DM particle position.
>     Can it be the origin of issue?
>
>
> I think this inquiry can go to enzo mailing list or MUSIC developer.
> If it is necessary, I can ask it to other place.
>
> Thank you in advance,
> Junhwan
>
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