There are a zillion resources on splines, but I can't seem to find this.

I need an algorithm for a smoothing (cubic) spline where the endpoint derivatives are specified (the so-called 'clamped spline').

With no smoothing (so just ordinary interpolation), there are many treatments.

With so-called 'natural' endpoints (second derivative is zero) + smoothing, there are many treatments.

Trying to not reinvent the wheel.

Does anyone know a link or a cite?