Construct a new piecewise polynomial representing the antiderivative.
nu : int, optional
Order of antiderivative to evaluate. Default is 1, i.e. compute the first integral. If negative, the derivative is returned.
bp : BPoly
Piecewise polynomial of order k + nu representing the antiderivative of this polynomial.
If antiderivative is computed and self.extrapolate='periodic', it will be set to False for the returned instance. This is done because the antiderivative is no longer periodic and its correct evaluation outside of the initially given x interval is difficult.