[yt-dev] .quantities issue

[Matthew Turk]

As a followup, this script (run on Mike's dataset):

http://paste.yt-project.org/show/2191/

gives results of:

5.793e+14 5.793e+14 5.640e+14
2.956e-14 1.336e-02

While the accumulated roundoff error here is ~1% (which is something
to be concerned about, and which I think we can start addressing by
mandating dtypes in our calls to things like .sum()) it's still not
the significant errors that are being reported.

I think quantities are okay.  (Which is good, because the testing
system should have caught any problems that would be introduced with
parallelism, and it did not.)  Additionally, I tested in HaloFinder in
both parallel and serial, and on line 2240 I inserted a print
statement indicating the received total volume.  I got the correct
answer in serial and in parallel.  Is this the issue you were seeing?

Could you please provide a small, minimally viable sample script that
can show the problem?

-Matt

On Fri, Feb 24, 2012 at 7:32 PM, Matthew Turk <matthewturk at gmail.com> wrote:
> Hi Stephen,
>
> On Fri, Feb 24, 2012 at 7:25 PM, Stephen Skory <s at skory.us> wrote:
>> Hi all,
>>
>> when I was trying to work on Mike's latest halo finder problem, I
>> tried swapping out the total_mass sum for a .quantities on this line:
>>
>> https://bitbucket.org/yt_analysis/yt/src/73fa0ace10e3/yt/analysis_modules/halo_finding/halo_objects.py#cl-2047
>>
>> but doing that seriously changed the answers. Digging a bit deeper I
>> see that for some reason, the same value is being fed in twice (I'm
>> using two cores) to mpi_allreduce, which gives the wrong total_mass
>> out. I see different values going into mpi_allreduce, and the correct
>> total_mass, when I use the original summing method. This has led me to
>> conclude that the .quantities is not being done correctly here -
>> there's something wrong with the multi-level parallelism here I
>> think... or something. Does anyone have any ideas of what could be
>> going on? Thanks!
>
> I'm not sure I understand -- is something wrong with
> *quantities-in-general*, or with the way it's being called in
> halo_objects?  Can you investigate with a small dataset if the answer
> changes based on manually calculating versus using quantities in
> serial & parallel?
>
> -Matt
>
>>
>> --
>> Stephen Skory
>> s at skory.us
>> http://stephenskory.com/
>> 510.621.3687 (google voice)
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