convinterp v0.2.0

Integrals of any order, in 1D and N-D.

New

• Integrals. A negative derivative order gives the integral of the interpolant: derivative=-1 is the antiderivative, -2 the twofold integral, and so on, up to order 8 for "b7" to "b13". Each integral is anchored at the first knot, where it and all lower integrals are zero.
• Mixed orders in N-D. Integrals can be combined with values and derivatives, one order per axis, e.g. derivative=(-1, 1).
• Fast and exact. Integrals are computed exactly from the kernels' polynomial pieces, converge at the kernel's interpolation order, and evaluate in constant time per point, about as fast as the interpolant itself.
• Documentation. An Integrals section in the user guide, a theory section on how integrals work, integral convergence and speed on the accuracy page, and a new Limitations section.

Breaking changes

None.

Migration guide

No changes needed. Negative derivative orders, which previously raised a ValueError, now return integrals.