[yt-users] Projection issue

[Britton Smith]

Hi Elizabeth,

The problem with calculating the mass from a projection of the mass field
is that you need to divide each projection pixel by the total path length
that cell has been projected.  With AMR, this is trickier because cells
with more refined child cells won't be used in the projection, so for each
value in proj you don't know the total path.  This does work with unigrid
data, so for example, this will give the right total mass:
(proj['CellMassMsun'] / proj['pdx']).sum() / pf.units['cm'] / 2

However, the following will work:
((2 * pf.units['cm'] * proj['pdx'])**2 * proj['Density']).sum() / 1.989e33
since the Density projection gives the column density.

I'm not sure what's going on with the fixed_res_proj.

Britton

On Thu, Apr 4, 2013 at 7:58 AM, Elizabeth Tasker <
tasker at astro1.sci.hokudai.ac.jp> wrote:

> Hello,
>
> I have 2 problems, but possibly I only need the solution to one :)
>
> (1) If I calculate the total mass in a simulation via the projection:
>
> projection = pf.h.proj(2, 'CellMass')
> sum(projection["CellMass"]/projection["pdx"]/2.0/3.08568025e18)
>
> (i.e. sum(sum(m_i*dl)/dl) )
>
> I get:  1.4855032022312827e+43
>
> However, if I just sum it directly:
>
> dd = pf.h.all_data()
> sum(dd["CellMass"])
>
> I get: 6.3279045575257765e+42
>
> I was expecting those two numbers to be approximately the same. Why are
> they very different? Have I misunderstood the value of pdx? I think it
> should be equal to half the integration step.
>
> (2) The second problem occurred when I tried to fix this by using a fixed
> resolution projection (in case a variable dl was the issue).
>
> I tried:
>
> proj = pf.h.fixed_res_proj(2, 0, [0, 0, 0], [128,128,128])
>
> (My root grid is 128^3)
>
> but I get:
>
> ValueError                                Traceback (most recent call last)
> /home/tasker/yt-new/src/yt-hg/scripts/iyt in <module>()
> ----> 1 proj = pf.h.fixed_res_proj(2, 0, [0, 0, 0], [128,128,128])
>
> /home/tasker/yt-new/src/yt-hg/yt/data_objects/data_containers.pyc in
> __init__(self, axis, level, left_edge, dims, fields, pf, **kwargs)
>    2460         self.domain_width = np.rint((self.pf.domain_right_edge -
>    2461
> self.pf.domain_left_edge)/self.dds).astype('int64')
> -> 2462         self._refresh_data()
>    2463
>    2464     def _get_list_of_grids(self):
>
> /home/tasker/yt-new/src/yt-hg/yt/data_objects/data_containers.pyc in
> _refresh_data(self)
>     318         """
>     319         self.clear_data()
> --> 320         self.get_data()
>     321
>     322     def keys(self):
>
> /home/tasker/yt-new/src/yt-hg/yt/data_objects/data_containers.pyc in
> get_data(self, fields)
>    2494         Iterates over the list of fields and generates/reads them
> all.
>    2495         """
> -> 2496         self._get_list_of_grids()
>    2497         if not self.has_key('pdx'):
>    2498             self._generate_coords()
>
> /home/tasker/yt-new/src/yt-hg/yt/data_objects/data_containers.pyc in
> _get_list_of_grids(self)
>    2470         else:
>    2471             grids,ind = self.pf.hierarchy.get_box_grids(
> -> 2472                             self.left_edge, self.right_edge)
>    2473         level_ind = (self.pf.hierarchy.grid_levels.ravel()[ind] <=
> self.level)
>    2474         sort_ind =
> np.argsort(self.pf.h.grid_levels.ravel()[ind][level_ind])
>
> /home/tasker/yt-new/src/yt-hg/yt/data_objects/object_finding_mixin.pyc in
> get_box_grids(self, left_edge, right_edge)
>     201         eps = np.finfo(np.float64).eps
>     202         grid_i = np.where((np.all((self.grid_right_edge -
> left_edge) > eps, axis=1)
> --> 203                          & np.all((right_edge -
> self.grid_left_edge) > eps, axis=1)) == True)
>     204
>     205         return self.grids[grid_i], grid_i
>
> ValueError: operands could not be broadcast together with shapes (3,3)
> (7100,3)
>
>
> What did I do wrong?
>
> Thank you!
>
> Elizabeth
>
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