parametric equation

Dear all,

I am wondering how to solve a parametric equation with dolfin if that's even possible. Let's say I want to solve
dX/dT = f(x) where T = T(x) is a function or parameter on the mesh and X=X(T) is also a function on the mesh but thru T. Hopefully this makes sense but this type of ode occur in optical geometry.

Thanks,
Chaffra