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[Patrick Riesen <priesen@xxxxxxxxxxxxxxx>]

hello,

i want to take the gradient of a coefficient with respect to some other 
quantity than the spatial coordinates (i.e. some other coefficient).

i tried to construct a custom operator derived from diff() and the 
SpatialCoordinate/Derivative classes in ufl but after some point beyond 
my knowledge it always gets evaluated to zero by FFC then stops 
compiling with FFC : division by zero!

does somebody of you experts know an approach to this?

many thanks and best regards,
patrick