Just so you know, there are very few situations where one should produce a graph from a set of points by spline interpolation (at least in the natural sciences)

Just so you know, there are very few situations where one should produce a graph from a set of points by spline interpolation (at least in the natural sciences). It almost never is the right choice, if you don't have a model for how the graph you are sampling looks like you shouldn't draw lines between points at all.