Hi Jingjing,

I'm sorry that you're running into some problems with yt.lagrangian_region. Let me see if I can help you.

The output of the code should return a box in code units containing all of the DM particles in the selected halo.  I've only tested this with enzo outputs (and I believe that is what you're using it on too), so those code units will go from 0 to 1 in x, y, z.  In addition to this output, the code also will recenter these coordinates so that the final halo coordinates will sit at 0.5, 0.5, 0.5 at the center of the box.  It provides the original box shifted over in coordinates to accomodate this recentering.  Lastly, you are correct that some of the coordinates will go above 1 in cases when the particles shift over the periodic boundary condition.

Do your results make more sense given this information?  If you're still confused, can you send us the text of your outputs, so that we can try to figure them out?

I'm actually working on a newer version of this which will work with yt 3.0 as part of a larger effort to make efficient zoom simulations, but I've not yet finished working on it.  I'll make sure to announce it here when this is complete and ready.

Cameron

On Tue, Oct 28, 2014 at 12:00 PM, Chen Jingjing <chenjj235@gmail.com> wrote:

Hi,

I am using the code yt.lagrangian_volume to trace the box that contains the dark matter particles at an early stage(higher redshift). But I was quite confused about the output. I am attaching the output file below. 

(1) I don't know what the values for the box in the new frame mean, i.e. what is the unit of these values? It seems to be the normalized scale because the values are about 1. But it does not seem to be normalized too because there are some values that are larger than 1. Is that due to the periodicity of the box?

(2) The bounding box and box in the new frame seems to have the same size. The difference between the two box is just translation. But I was expecting that the box should be expanding/collapsing.

(3) The COM (center of mass) in the output is within neither of the box.

Does anyone know how to explain the box values in the output file?

Thanks,
Jingjing

--

Jingjing Chen [ chenjj235@gmail.com ]
Department of Astronomy
Columbia University
550 West 120th Street
New York, New York 10027
Cell Phone: +1(347)5746709

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--
Cameron Hummels

Postdoctoral Researcher

Steward Observatory

University of Arizona

http://chummels.org