Construct a new piecewise polynomial representing the derivative.
nu : int, optional
Order of derivative to evaluate. (Default: 1) If negative, the antiderivative is returned.
pp : PPoly
Piecewise polynomial of order k2 = k - 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 are considered half-open, [a, b), except for the last interval which is closed [a, b].