not-a-knot boundary conditions for cubic spline interpolation

[Simon Wiesheier]

Dear all,

is there support for 1d cubic spline interpolation with not-a-knot boundary
conditions?
I could only find the interpolation types
-gsl_interp_cspline
-gsl_interp_cspline_periodic

I wanted to double-check that, maybe I missed some parts of the manual.

My issue is that the interpolated function must be convex, but better
strictly convex with positive 2nd derivatives.

Best
Simon