[yt-users] Variance in phase/profiles

Matthew Turk matthewturk at gmail.com
Wed Oct 5 09:13:08 PDT 2011


Hi Dave,

I've thought about this on and off and there is an oustanding bug:

https://bitbucket.org/yt_analysis/yt/issue/277/standard-deviation-for-1d-profiles

One option is also to simply do it yourself by not using lazy_reader,
and loading the data manually.  (Cameron has done this, sort of.)
Another is to use a running-stddev algorithm, like one of those listed
here:

http://www.strchr.com/standard_deviation_in_one_pass

If you want to look at this more in depth, please feel free to either
ping yt-dev or leave comments in the ticket.  It'd be a great addition
to have.

-Matt

On Wed, Oct 5, 2011 at 12:01 PM, Britton Smith <brittonsmith at gmail.com> wrote:
> Hi Dave,
>
> The best I have been able to do for this is to manually bin up a 3d data
> object with the cut_region function and then do the calculation myself bin
> by bin.
> For example, if you have a sphere, you can do
> new_sphere = sphere.cut_region(['grid["Temperature"] > 1e5',
> 'grid["Temperature"] < 1e6'])
> That'll give you access to all the cells within that bin for a variance
> calculation.  Note the quotes around those expressions.  The cuts are
> applied in yt using eval functions.
>
> This will work, but it's slow and requires you to do a lot by hand.
>
> Britton
>
> On Wed, Oct 5, 2011 at 11:51 AM, david collins <antpuncher at gmail.com> wrote:
>>
>> Hi, Everybody!
>>
>> Does anyone out there have a technique for getting the variance out of
>> a profile object?  A profile object is good at getting <X> vs. B, I'd
>> then like to get < (X - <X>)^2 > vs B.  Matt and I had spittballed the
>> possibility some time ago, but I was wondering if anyone out there had
>> successfully done it.
>>
>> Thanks,
>> d.
>>
>> --
>> Sent from my computer.
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>
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