Provide a routine for computing derivatives of order higher than one in spline evaluator classes #809
Description
Description
It is currently possible to evaluate first order derivatives of a scalar field by using its spline representation, with the SplineEvaluator and SplineEvaluator2D classes.
The derivatives can be obtained from the deriv_dim_1 and deriv_dim_2 methods of the SplineEvaluator2D class, and from the deriv method of the SplineEvaluator class.
It would be very useful to update these functions so that they could take an additional parameter (say an int derivative_order with default value one) that would specify the degree of the derivative.
Exemple usecase
In the gyselalibxx library the DiscreteToCartesian class represents a mapping from a general system of coordinates defined by a spline. It is necessary to add to this class a method to compute the derivative of the Jacobian (for instance to be able to compute efficienty the divergence operator). The derivative of the Jacobian involves second order derivatives of the spline used to define the mapping.