Construct a new piecewise polynomial representing the derivative.
nu : ndim-tuple of int
Order of derivatives to evaluate for each dimension. If negative, the antiderivative is returned.
pp : NdPPoly
Piecewise polynomial of orders (k - nu, ..., k[n] - nu[n]) representing the derivative of this polynomial.
Derivatives are evaluated piecewise for each polynomial segment, even if the polynomial is not differentiable at the breakpoints. The polynomial intervals in each dimension are considered half-open, [a, b), except for the last interval which is closed [a, b].