[yt-users] data along rays

[Elizabeth Tasker]

Hi,

I have a mystery:

Creating a ray via:

 ray = pf.h.ray( com[c], com[nearestcore])

and I want to get the effective potential along it, for which I have a 
subrountine for. However, yr gets stuck here:

 if data.pf["HydroMethod"] == 2:
        xvel[0:-1,0:-1,0:-1] = 
0.5*(data["x-velocity"][slice(None,-1,None),0:-1,0:-1]+data["x-velocity"][slice(1,None,None),0:-1,0:-1])


I thought the problem was because a ray is a 1D data set and I was 
trying to treat it like a 3D array, but what confuses me is that:

ray["DivV"]

works just fine but as the same sort of line within its definition.

http://yt.enzotools.org/doc/reference/field_list.html#divv

To make matters more confusing, if I copy out the definition of DivV 
directly from universal_fields.py and implement it imaginatively as 
DivV2, the code doesn't work, giving me:

/1/home/taskere/yt/scripts/iyt in _DivV2(field, data)
    211         div_fac = 2.0
    212     ds = div_fac * data['dx'].flat[0]
--> 213     f  = data["x-velocity"][sl_right,1:-1,1:-1]/ds
    214     f -= data["x-velocity"][sl_left ,1:-1,1:-1]/ds
    215     if data.pf.dimensionality > 1:

IndexError: too many indices


What magic line does yt have to allow DivV to work for a ray?

Thanks,

Elizabeth