[yt-users] field gradients / vorticity / ghost cells

[Andrew Cunningham]

Thanks, David.  That does help.

On Thu, 27 May 2010, David Collins wrote:

> The best place to look is in yt/lagos/UniversalFields.py, and look at
> the DivV example.  That takes one ghost zone on the 3 velocity
> components.  I've pasted it below for convenience
>
> The HydroMethod business at the top is to switch between the cell
> centered PPM (HydroMethod==0) or the staggered face-centered Zeus data
> (HydroMethod == 2)
>
> The object that 'data' then returns is larger than the grid patch it
> represents in each direction by the number passed to ValidateSpatial.
> ValidateSpatial gets passed to add_field with the Validators argument,
> and expects the number of ghost zones and the list of fields to get
> ghost zones for.
>
> Hope that helps,
> d.
>
>
> def _DivV(field, data):
>    # We need to set up stencils
>    if data.pf["HydroMethod"] == 2:
>        sl_left = slice(None,-2,None)
>        sl_right = slice(1,-1,None)
>        div_fac = 1.0
>    else:
>        sl_left = slice(None,-2,None)
>        sl_right = slice(2,None,None)
>        div_fac = 2.0
>    ds = div_fac * data['dx'].flat[0]
>    f  = data["x-velocity"][sl_right,1:-1,1:-1]/ds
>    f -= data["x-velocity"][sl_left ,1:-1,1:-1]/ds
>    ds = div_fac * data['dy'].flat[0]
>    f += data["y-velocity"][1:-1,sl_right,1:-1]/ds
>    f -= data["y-velocity"][1:-1,sl_left ,1:-1]/ds
>    ds = div_fac * data['dz'].flat[0]
>    f += data["z-velocity"][1:-1,1:-1,sl_right]/ds
>    f -= data["z-velocity"][1:-1,1:-1,sl_left ]/ds
>    new_field = na.zeros(data["x-velocity"].shape, dtype='float64')
>    new_field[1:-1,1:-1,1:-1] = f
>    return new_field
> def _convertDivV(data):
>    return data.convert("cm")**-1.0
> add_field("DivV", function=_DivV,
>            validators=[ValidateSpatial(1,
>            ["x-velocity","y-velocity","z-velocity"])],
>          units=r"\rm{s}^{-1}", take_log=False,
>          convert_function=_convertDivV)
>
>
> On Thu, May 27, 2010 at 3:48 PM, Andrew Cunningham
> <ajc4 at pas.rochester.edu> wrote:
>> I'd like to make a derived field that is the gradient of a primitive field.
>>  Is there an example of how I can do this?  I'm not sure how to handle ghost
>> cells for something like this.
>>
>> I spoke with Jeff and he indicated that there was a vorticity example
>> somewhere, but I cannot find it.
>>
>> Thanks.
>>
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>>
>
>
>
> -- 
> Sent from my Stone Tablet and carried by my Pterodactyl.
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