How about this one? (The green curve does not look like monotonic to me though ... The blue curve is the reference you cited)
MESA/INTERP_1D monotonicity preserving cubic interpolation piecewise monotonic cubic interpolation http://mesa.sourceforge.net/interp_1D.html On Thu, Mar 1, 2012 at 1:30 PM, Christian Krueger <mangrove...@gmail.com> wrote: > > Hi... is there any possibility to get a strictly monotone interpolation function? > > I have data which for sure have to be monotone, but the provided interpolation methods (cspline, akima) do not preserve this condition (linear interpolation is not smooth and polynomial of course useless with 200+ datapoints). > > I wonder whether the method of Steffen (1990) is implemented somewhere which seem to have some nice features (monotonicity, almost no spurious oscillations)? Or might it be a useful extension for GSL? > Found in this paper: A simple method for monotonic interpolation in one dimension, Astron. Astrophys. 239, 443 (1990) > > > Regards, > Christian >