Hi, I am currently using a ROOT::Math::Interpolator, but it only provides a small set of hardcoded interpolation types (Linear, Cubic Spline, Akima & ceriodic variants). Currently these methods are failing me because I require monotone interpolation (actually the Linear one is monotone, but it gives bad derivatives). I have found that there are a few well-understood monotone interpolation techniques (my favourite: adsabs.harvard.edu/full/1990A%26A…239…443S)
Given that GSL is considered “feature complete”, it would be very difficult to add an interpolation method to GSL itself. They recommend that enhancements be provided by external packages.
So my question is: how difficult would it be to implement Steffen (1990) interpolation as a ROOT extension to the existing GSL interpolation methods? I’ve never contributed anything but bug reports to ROOT, so even the process of submitting patches seems opaque. Is it even possible to add a non-GSL interpolator given the structure of ROOT::Math::Interpolator?