[yt-users] Field based on neighbour cells

[Nathan Goldbaum]

On Fri, Dec 19, 2014 at 10:14 AM, José Utreras <jutreras at das.uchile.cl>
wrote:
>
> Thanks for your answer John
> I have to define sl_right, sl_center :global name 'sl_right' is not
> defined
>
> I'm not really sure how to do it. I want to do something like these:
>
> vx = data["gas", "velocity_x"][sl_right,sl_center,sl_center]
> vx+= data["gas", "velocity_x"][sl_center,sl_right,sl_center]
>

Hi Jose,

This code looks like came from the definition of the vorticity field.
You're correct that ftype, sl_right, sl_center, and sl_left aren't defined
inside the voriticity field definition.  That's because the voriticity
field is a closure (a special type of python function that is able to use
varibles defined in the enclosing scope around the function definition).
I'd encourage you to take a look at yt/fields/fluid_vector_fields.py to see
how this works inside yt:

https://bitbucket.org/yt_analysis/yt/src/5007c9a46622118abab89dc153dbfb6591cc5177/yt/fields/fluid_vector_fields.py?at=yt


> ...
>
> add the x velocity of 6 neighbour cells.
>
>
Your field definition will need a ValidateSpatial field validator (like
vorticity). ValidateSpatial will make it so data is passed into a field
definition along with a user-selectable number of ghost zones.



> Thanks
>
>
> 2014-12-19 13:31 GMT-03:00 John ZuHone <jzuhone at gmail.com>:
>
>> Jose,
>>
>> Presuming that you have sl_right and sl_center defined in your field
>> already, you should be able to just substitute “gas” for ftype, since the
>> velocity fields are “gas" fields.
>>
>> Best,
>>
>> John
>>
>> > On Dec 19, 2014, at 11:04 AM, José Utreras <jutreras at das.uchile.cl>
>> wrote:
>> >
>> > Hi everyone,
>> >
>> > I want to write a new field based on the neighbour cells like this:
>> >
>> > vx = data[ftype, "velocity_x"][sl_right,sl_center,sl_center]
>> >
>> > but I got " global name 'ftype' is not defined". I suppose that I have
>> the same problem with sl_left, sl_right , sl_center.
>> >
>> > Thanks,
>> >
>> > Jose
>> > _______________________________________________
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