[yt-users] Error with derived field

Hello, I am having trouble using a derived field with a CoveringGrid. I am making fields for dPhi/dx, dPhi/dy, dPhi/dz using the PotentialField from ENZO. The derivative fields do not get passed into the CoveringGrid and get recalculated. This leads to the derivative being zero in areas that were originally in coarse cells. Density and DivV fields were passed to the CoveringGrid properly. As a test I defined a field that was Density^2 and that was passed to the CoveringGrid properly, so I think it is a problem specific to derived fields based on the ENZO-specific PotentialField. I have included the source for my derivative functions. Thank you, Nathan Butcher