Make derivative of AnalyticGridFunction bound to an element if the GridFunction itself is bound
Summary
This MR modifies the derivative()
function of LocalAnalyticGridFunction
such that it returns a bound local-function if the underlying value-local-function was bound before, i.e., the bound-to element is passed to the derivative and a corresponding geometry is automatically constructed.
This is an implementation of the discussion in #69 (closed)